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)

v3.19.3
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
Sep. 30, 2019
Dec. 31, 2018
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost $ 193,623 $ 221,454
Fair Value 195,260 220,645
Short-term investments [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost 124,227 137,532
Gross Unrealized Gains 249 7
Gross Unrealized Losses (1) (103)
Fair Value 124,475 137,436
Short-term investments [Member] | U.S. Treasuries [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost 109,208 121,252
Gross Unrealized Gains 192 7
Gross Unrealized Losses (1) (79)
Fair Value 109,399 121,180
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 15,019 11,962
Gross Unrealized Gains 57 0
Gross Unrealized Losses 0 (11)
Fair Value 15,076 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 69,396 83,922
Gross Unrealized Gains 1,420 143
Gross Unrealized Losses (31) (856)
Fair Value 70,785 83,209
Long-term marketable securities [Member] | U.S. Treasuries [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost 30,146 44,997
Gross Unrealized Gains 325 128
Gross Unrealized Losses (15) (115)
Fair Value 30,456 45,010
Long-term marketable securities [Member] | U.S. Government Sponsored Entities [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost 1,415 1,569
Gross Unrealized Gains 2 0
Gross Unrealized Losses (4) (62)
Fair Value 1,413 1,507
Long-term marketable securities [Member] | Corporate debt securities [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost 29,870 32,467
Gross Unrealized Gains 980 3
Gross Unrealized Losses (8) (633)
Fair Value 30,842 31,837
Long-term marketable securities [Member] | Asset-backed securities and other [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost 7,965 4,889
Gross Unrealized Gains 113 12
Gross Unrealized Losses (4) (46)
Fair Value $ 8,074 $ 4,855