Annual report pursuant to Section 13 and 15(d)

Fair Value Measurements - Schedule of Assets and Liabilities at Fair Value on Recurring Basis (Detail)

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Fair Value Measurements - Schedule of Assets and Liabilities at Fair Value on Recurring Basis (Detail) - USD ($)
$ in Thousands
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Assets held in rabbi trust $ 9,452 $ 8,268  
Marketable securities, available for sale 211,561 220,645  
Deferred compensation liability 8,241 7,893  
Short-term investments [Member]      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Marketable securities, available for sale 150,752 137,436  
Long-term marketable securities [Member]      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Marketable securities, available for sale 60,809 83,209  
U.S. Treasuries [Member] | Short-term investments [Member]      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Marketable securities, available for sale 124,580 121,180  
U.S. Treasuries [Member] | Long-term marketable securities [Member]      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Marketable securities, available for sale 24,423 45,010  
U.S. Government Sponsored Entities [Member] | Short-term investments [Member]      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Marketable securities, available for sale 0 3,505  
U.S. Government Sponsored Entities [Member] | Long-term marketable securities [Member]      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Marketable securities, available for sale 1,355 1,507  
Corporate debt securities [Member] | Short-term investments [Member]      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Marketable securities, available for sale 26,172 11,951  
Corporate debt securities [Member] | Long-term marketable securities [Member]      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Marketable securities, available for sale 26,471 31,837  
Asset-backed securities and other [Member] | Short-term investments [Member]      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Marketable securities, available for sale 0 800  
Asset-backed securities and other [Member] | Long-term marketable securities [Member]      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Marketable securities, available for sale 8,560 4,855  
Recurring [Member]      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Cash and cash equivalents 190,600 164,725  
Recurring [Member] | Short-term investments [Member]      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Marketable securities, available for sale 150,752 137,436  
Recurring [Member] | Long-term marketable securities [Member]      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Marketable securities, available for sale 60,809 83,209  
Recurring [Member] | Commercial Paper and Other [Member]      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Cash and cash equivalents 5,087 1,599  
Recurring [Member] | Money market funds [Member]      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Cash and cash equivalents 185,513 163,126  
Recurring [Member] | Assets held in rabbi trust [Member]      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Assets held in rabbi trust 9,452 8,268  
Recurring [Member] | U.S. Treasuries [Member] | Short-term investments [Member]      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Marketable securities, available for sale 124,580 121,180  
Recurring [Member] | U.S. Treasuries [Member] | Long-term marketable securities [Member]      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Marketable securities, available for sale 24,423 45,010  
Recurring [Member] | U.S. Government Sponsored Entities [Member] | Short-term investments [Member]      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Marketable securities, available for sale 0 3,505  
Recurring [Member] | U.S. Government Sponsored Entities [Member] | Long-term marketable securities [Member]      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Marketable securities, available for sale 1,355 1,507  
Recurring [Member] | Corporate debt securities [Member] | Short-term investments [Member]      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Marketable securities, available for sale 26,172 11,951  
Recurring [Member] | Corporate debt securities [Member] | Long-term marketable securities [Member]      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Marketable securities, available for sale 26,471 31,837  
Recurring [Member] | Asset-backed securities and other [Member] | Short-term investments [Member]      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Marketable securities, available for sale 0 800  
Recurring [Member] | Asset-backed securities and other [Member] | Long-term marketable securities [Member]      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Marketable securities, available for sale 8,560 4,855  
Level 1 [Member]      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Deferred compensation liability 8,241 7,893  
Level 1 [Member] | Recurring [Member]      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Cash and cash equivalents 185,513 164,725  
Level 1 [Member] | Recurring [Member] | Short-term investments [Member]      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Marketable securities, available for sale 124,580 121,180  
Level 1 [Member] | Recurring [Member] | Long-term marketable securities [Member]      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Marketable securities, available for sale 24,423 45,010  
Level 1 [Member] | Recurring [Member] | Commercial Paper and Other [Member]      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Cash and cash equivalents 0 1,599  
Level 1 [Member] | Recurring [Member] | Money market funds [Member]      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Cash and cash equivalents 185,513 163,126  
Level 1 [Member] | Recurring [Member] | Assets held in rabbi trust [Member]      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Assets held in rabbi trust 0 0  
Level 1 [Member] | Recurring [Member] | U.S. Treasuries [Member] | Short-term investments [Member]      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Marketable securities, available for sale 124,580 121,180  
Level 1 [Member] | Recurring [Member] | U.S. Treasuries [Member] | Long-term marketable securities [Member]      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Marketable securities, available for sale 24,423 45,010  
Level 1 [Member] | Recurring [Member] | U.S. Government Sponsored Entities [Member] | Short-term investments [Member]      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Marketable securities, available for sale 0 0  
Level 1 [Member] | Recurring [Member] | U.S. Government Sponsored Entities [Member] | Long-term marketable securities [Member]      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Marketable securities, available for sale 0 0  
Level 1 [Member] | Recurring [Member] | Corporate debt securities [Member] | Short-term investments [Member]      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Marketable securities, available for sale 0 0  
Level 1 [Member] | Recurring [Member] | Corporate debt securities [Member] | Long-term marketable securities [Member]      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Marketable securities, available for sale 0 0  
Level 1 [Member] | Recurring [Member] | Asset-backed securities and other [Member] | Short-term investments [Member]      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Marketable securities, available for sale 0 0  
Level 1 [Member] | Recurring [Member] | Asset-backed securities and other [Member] | Long-term marketable securities [Member]      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Marketable securities, available for sale 0 0  
Level 2 [Member]      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Deferred compensation liability 0 0  
Level 2 [Member] | Recurring [Member]      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Cash and cash equivalents 5,087 0  
Level 2 [Member] | Recurring [Member] | Short-term investments [Member]      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Marketable securities, available for sale 26,172 16,256  
Level 2 [Member] | Recurring [Member] | Long-term marketable securities [Member]      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Marketable securities, available for sale 36,386 38,199  
Level 2 [Member] | Recurring [Member] | Commercial Paper and Other [Member]      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Cash and cash equivalents 5,087 0  
Level 2 [Member] | Recurring [Member] | Money market funds [Member]      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Cash and cash equivalents 0 0  
Level 2 [Member] | Recurring [Member] | Assets held in rabbi trust [Member]      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Assets held in rabbi trust 9,452 8,268  
Level 2 [Member] | Recurring [Member] | U.S. Treasuries [Member] | Short-term investments [Member]      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Marketable securities, available for sale 0 0  
Level 2 [Member] | Recurring [Member] | U.S. Treasuries [Member] | Long-term marketable securities [Member]      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Marketable securities, available for sale 0 0  
Level 2 [Member] | Recurring [Member] | U.S. Government Sponsored Entities [Member] | Short-term investments [Member]      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Marketable securities, available for sale 0 3,505  
Level 2 [Member] | Recurring [Member] | U.S. Government Sponsored Entities [Member] | Long-term marketable securities [Member]      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Marketable securities, available for sale 1,355 1,507  
Level 2 [Member] | Recurring [Member] | Corporate debt securities [Member] | Short-term investments [Member]      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Marketable securities, available for sale 26,172 11,951  
Level 2 [Member] | Recurring [Member] | Corporate debt securities [Member] | Long-term marketable securities [Member]      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Marketable securities, available for sale 26,471 31,837  
Level 2 [Member] | Recurring [Member] | Asset-backed securities and other [Member] | Short-term investments [Member]      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Marketable securities, available for sale 0 800  
Level 2 [Member] | Recurring [Member] | Asset-backed securities and other [Member] | Long-term marketable securities [Member]      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Marketable securities, available for sale 8,560 4,855  
Level 3 [Member]      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Deferred compensation liability 0 0  
Level 3 [Member] | Recurring [Member]      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Cash and cash equivalents 0 0  
Level 3 [Member] | Recurring [Member] | Short-term investments [Member]      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Marketable securities, available for sale 0 0  
Level 3 [Member] | Recurring [Member] | Long-term marketable securities [Member]      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Marketable securities, available for sale 0 0  
Level 3 [Member] | Recurring [Member] | Commercial Paper and Other [Member]      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Cash and cash equivalents 0 0  
Level 3 [Member] | Recurring [Member] | Money market funds [Member]      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Cash and cash equivalents 0 0  
Level 3 [Member] | Recurring [Member] | Assets held in rabbi trust [Member]      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Assets held in rabbi trust 0    
Level 3 [Member] | Recurring [Member] | U.S. Treasuries [Member] | Short-term investments [Member]      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Marketable securities, available for sale 0 0  
Level 3 [Member] | Recurring [Member] | U.S. Treasuries [Member] | Long-term marketable securities [Member]      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Marketable securities, available for sale 0 0  
Level 3 [Member] | Recurring [Member] | U.S. Government Sponsored Entities [Member] | Short-term investments [Member]      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Marketable securities, available for sale 0 0  
Level 3 [Member] | Recurring [Member] | U.S. Government Sponsored Entities [Member] | Long-term marketable securities [Member]      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Marketable securities, available for sale 0 0  
Level 3 [Member] | Recurring [Member] | Corporate debt securities [Member] | Short-term investments [Member]      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Marketable securities, available for sale 0 0  
Level 3 [Member] | Recurring [Member] | Corporate debt securities [Member] | Long-term marketable securities [Member]      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Marketable securities, available for sale 0 0  
Level 3 [Member] | Recurring [Member] | Asset-backed securities and other [Member] | Short-term investments [Member]      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Marketable securities, available for sale 0 0  
Level 3 [Member] | Recurring [Member] | Asset-backed securities and other [Member] | Long-term marketable securities [Member]      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Marketable securities, available for sale 0 0  
Contingent Consideration [Member]      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Contingent consideration 4,788 2,875 $ 0
Contingent Consideration [Member] | Level 1 [Member] | Recurring [Member]      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Contingent consideration 0 0  
Contingent Consideration [Member] | Level 2 [Member] | Recurring [Member]      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Contingent consideration 0 0  
Contingent Consideration [Member] | Level 3 [Member]      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Contingent consideration $ 4,788 $ 2,875