Annual report pursuant to Section 13 and 15(d)

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

v3.6.0.2
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
Dec. 31, 2016
Dec. 31, 2015
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost $ 105,365 $ 135,201
Fair Value 104,929 134,255
Short-term investments [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost 27,484 79,943
Gross Unrealized Gains 0 0
Gross Unrealized Losses (30) (83)
Fair Value 27,454 79,860
Short-term investments [Member] | U.S. Treasuries [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost 24,987 62,343
Gross Unrealized Gains 0 0
Gross Unrealized Losses (30) (71)
Fair Value 24,957 62,272
Short-term investments [Member] | U.S. Government Sponsored Entities [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost 2,497 17,571
Gross Unrealized Gains 0 0
Gross Unrealized Losses 0 (12)
Fair Value 2,497 17,559
Short-term investments [Member] | Asset-backed securities and other [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost 0 29
Gross Unrealized Gains 0 0
Gross Unrealized Losses 0 0
Fair Value 0 29
Long-term marketable securities [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost 77,881 55,258
Gross Unrealized Gains 92 5
Gross Unrealized Losses (498) (868)
Fair Value 77,475 54,395
Long-term marketable securities [Member] | U.S. Treasuries [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost 40,865 15,283
Gross Unrealized Gains 0 0
Gross Unrealized Losses (229) (112)
Fair Value 40,636 15,171
Long-term marketable securities [Member] | U.S. Government Sponsored Entities [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost 12,618 12,107
Gross Unrealized Gains 0 0
Gross Unrealized Losses (58) (85)
Fair Value 12,560 12,022
Long-term marketable securities [Member] | Corporate debt securities [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost 17,841 17,219
Gross Unrealized Gains 74 5
Gross Unrealized Losses (165) (519)
Fair Value 17,750 16,705
Long-term marketable securities [Member] | Asset-backed securities and other [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost 6,557 10,649
Gross Unrealized Gains 18 0
Gross Unrealized Losses (46) (152)
Fair Value $ 6,529 $ 10,497