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)

v3.10.0.1
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, 2018
Dec. 31, 2017
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost $ 118,388 $ 125,761
Fair Value 117,403 125,659
Short-term investments [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost 85,664 73,659
Gross Unrealized Gains 0 0
Gross Unrealized Losses (178) (99)
Fair Value 85,486 73,560
Short-term investments [Member] | U.S. Treasuries [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost 74,147 57,712
Gross Unrealized Gains 0 0
Gross Unrealized Losses (136) (88)
Fair Value 74,011 57,624
Short-term investments [Member] | U.S. Government Sponsored Entities [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost 3,510 7,016
Gross Unrealized Gains 0 0
Gross Unrealized Losses (27) (8)
Fair Value 3,483 7,008
Short-term investments [Member] | Corporate debt securities [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost 7,907 8,931
Gross Unrealized Gains 0 0
Gross Unrealized Losses (15) (3)
Fair Value 7,892 8,928
Short-term investments [Member] | Asset-backed securities and other [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost 100 0
Gross Unrealized Gains 0 0
Gross Unrealized Losses 0 0
Fair Value 100 0
Long-term marketable securities [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost 32,724 52,102
Gross Unrealized Gains 5 292
Gross Unrealized Losses (812) (295)
Fair Value 31,917 52,099
Long-term marketable securities [Member] | U.S. Treasuries [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost 3,726 18,111
Gross Unrealized Gains 0 7
Gross Unrealized Losses (169) (164)
Fair Value 3,557 17,954
Long-term marketable securities [Member] | U.S. Government Sponsored Entities [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost 1,663 5,306
Gross Unrealized Gains 0 0
Gross Unrealized Losses (73) (62)
Fair Value 1,590 5,244
Long-term marketable securities [Member] | Corporate debt securities [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost 20,614 22,505
Gross Unrealized Gains 0 268
Gross Unrealized Losses (513) (54)
Fair Value 20,101 22,719
Long-term marketable securities [Member] | Asset-backed securities and other [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost 6,721 6,180
Gross Unrealized Gains 5 17
Gross Unrealized Losses (57) (15)
Fair Value $ 6,669 $ 6,182