Quarterly report pursuant to Section 13 or 15(d)

Investments in Marketable Securities - Schedule of Amortized Cost and Fair Value of Marketable Securities, Available-for-Sale, by Type of Security (Detail)

v3.19.2
Investments in Marketable Securities - Schedule of Amortized Cost and Fair Value of Marketable Securities, Available-for-Sale, by Type of Security (Detail) - USD ($)
$ in Thousands
Jun. 30, 2019
Dec. 31, 2018
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost $ 197,792 $ 221,454
Fair Value 199,238 220,645
Short-term investments [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost 118,744 137,532
Gross Unrealized Gains 169 7
Gross Unrealized Losses (4) (103)
Fair Value 118,909 137,436
Short-term investments [Member] | U.S. Treasuries [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost 95,607 121,252
Gross Unrealized Gains 143 7
Gross Unrealized Losses 0 (79)
Fair Value 95,750 121,180
Short-term investments [Member] | U.S. Government Sponsored Entities [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost 0 3,512
Gross Unrealized Gains 0 0
Gross Unrealized Losses 0 (7)
Fair Value 0 3,505
Short-term investments [Member] | Corporate debt securities [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost 23,137 11,962
Gross Unrealized Gains 26 0
Gross Unrealized Losses (4) (11)
Fair Value 23,159 11,951
Short-term investments [Member] | Asset-backed securities and other [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost 0 806
Gross Unrealized Gains 0 0
Gross Unrealized Losses 0 (6)
Fair Value 0 800
Long-term marketable securities [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost 79,048 83,922
Gross Unrealized Gains 1,310 143
Gross Unrealized Losses (29) (856)
Fair Value 80,329 83,209
Long-term marketable securities [Member] | U.S. Treasuries [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost 37,139 44,997
Gross Unrealized Gains 393 128
Gross Unrealized Losses (1) (115)
Fair Value 37,531 45,010
Long-term marketable securities [Member] | U.S. Government Sponsored Entities [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost 1,478 1,569
Gross Unrealized Gains 0 0
Gross Unrealized Losses (18) (62)
Fair Value 1,460 1,507
Long-term marketable securities [Member] | Corporate debt securities [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost 32,967 32,467
Gross Unrealized Gains 826 3
Gross Unrealized Losses (5) (633)
Fair Value 33,788 31,837
Long-term marketable securities [Member] | Asset-backed securities and other [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost 7,464 4,889
Gross Unrealized Gains 91 12
Gross Unrealized Losses (5) (46)
Fair Value $ 7,550 $ 4,855