Quarterly report pursuant to Section 13 or 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
Sep. 30, 2020
Dec. 31, 2019
Sep. 30, 2019
Dec. 31, 2018
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]        
Assets held in rabbi trust $ 9,467 $ 9,452    
Marketable debt securities, available for sale 216,018 211,561    
Deferred consideration 5,352 1,390    
Deferred compensation liability 7,914 8,241    
Short-term investments [Member]        
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]        
Marketable debt securities, available for sale 169,513 150,752    
Long-term marketable securities [Member]        
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]        
Marketable debt securities, available for sale 46,505 60,809    
U.S. Treasuries [Member] | Short-term investments [Member]        
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]        
Marketable debt securities, available for sale 93,641 124,580    
U.S. Treasuries [Member] | Long-term marketable securities [Member]        
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]        
Marketable debt securities, available for sale 3,689 24,423    
U.S. Government Sponsored Entities [Member] | Short-term investments [Member]        
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]        
Marketable debt securities, available for sale 37,740 0    
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 debt securities, available for sale 1,269 1,355    
Corporate debt securities [Member] | Short-term investments [Member]        
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]        
Marketable debt securities, available for sale 38,132 26,172    
Corporate debt securities [Member] | Long-term marketable securities [Member]        
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]        
Marketable debt securities, available for sale 34,357 26,471    
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 debt securities, available for sale 7,190 8,560    
Recurring [Member]        
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]        
Cash and cash equivalents 132,995 190,600    
Recurring [Member] | Short-term investments [Member]        
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]        
Marketable debt securities, available for sale 169,513 150,752    
Recurring [Member] | Long-term marketable securities [Member]        
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]        
Marketable debt securities, available for sale 46,505 60,809    
Recurring [Member] | Commercial Paper and Other [Member]        
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]        
Cash and cash equivalents 2,950 5,087    
Recurring [Member] | Money market funds [Member]        
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]        
Cash and cash equivalents 130,045 185,513    
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 9,467 9,452    
Recurring [Member] | U.S. Treasuries [Member] | Short-term investments [Member]        
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]        
Marketable debt securities, available for sale 93,641 124,580    
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 debt securities, available for sale 3,689 24,423    
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 debt securities, available for sale 37,740 0    
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 debt securities, available for sale 1,269 1,355    
Recurring [Member] | Corporate debt securities [Member] | Short-term investments [Member]        
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]        
Marketable debt securities, available for sale 38,132 26,172    
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 debt securities, available for sale 34,357 26,471    
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 debt securities, available for sale 7,190 8,560    
Level 1 [Member]        
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]        
Deferred consideration 0 0    
Deferred compensation liability 7,914 8,241    
Level 1 [Member] | Recurring [Member]        
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]        
Cash and cash equivalents 130,045 185,513    
Level 1 [Member] | Recurring [Member] | Short-term investments [Member]        
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]        
Marketable debt securities, available for sale 93,641 124,580    
Level 1 [Member] | Recurring [Member] | Long-term marketable securities [Member]        
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]        
Marketable debt securities, available for sale 3,689 24,423    
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 0    
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 130,045 185,513    
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 debt securities, available for sale 93,641 124,580    
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 debt securities, available for sale 3,689 24,423    
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 debt 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 debt 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 debt 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 debt 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 debt securities, available for sale 0 0    
Level 2 [Member]        
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]        
Deferred consideration 5,352 1,390    
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 2,950 5,087    
Level 2 [Member] | Recurring [Member] | Short-term investments [Member]        
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]        
Marketable debt securities, available for sale 75,872 26,172    
Level 2 [Member] | Recurring [Member] | Long-term marketable securities [Member]        
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]        
Marketable debt securities, available for sale 42,816 36,386    
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 2,950 5,087    
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 9,467 9,452    
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 debt 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 debt 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 debt securities, available for sale 37,740 0    
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 debt securities, available for sale 1,269 1,355    
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 debt securities, available for sale 38,132 26,172    
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 debt securities, available for sale 34,357 26,471    
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 debt securities, available for sale 7,190 8,560    
Level 3 [Member]        
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]        
Deferred consideration 0 0    
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 debt 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 debt 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 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 debt 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 debt 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 debt 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 debt 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 debt 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 debt 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 debt securities, available for sale 0 0    
Contingent Consideration [Member]        
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]        
Contingent consideration 4,683 3,387 $ 2,864 $ 2,875
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 $ 4,683 $ 3,387