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)

v3.4.0.3
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
Mar. 31, 2016
Dec. 31, 2015
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost $ 131,935 $ 135,201
Fair Value 132,120 134,255
Short-term investments [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost 75,108 79,943
Gross Unrealized Gains 7 0
Gross Unrealized Losses (3) (83)
Fair Value 75,112 79,860
Short-term investments [Member] | U.S. Treasuries [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost 61,040 62,343
Gross Unrealized Gains 7 0
Gross Unrealized Losses (1) (71)
Fair Value 61,046 62,272
Short-term investments [Member] | U.S. Government Sponsored Entities [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost 14,068 17,571
Gross Unrealized Gains 0 0
Gross Unrealized Losses (2) (12)
Fair Value 14,066 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 56,827 55,258
Gross Unrealized Gains 463 5
Gross Unrealized Losses (282) (868)
Fair Value 57,008 54,395
Long-term marketable securities [Member] | U.S. Treasuries [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost 18,333 15,283
Gross Unrealized Gains 103 0
Gross Unrealized Losses (2) (112)
Fair Value 18,434 15,171
Long-term marketable securities [Member] | U.S. Government Sponsored Entities [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost 10,943 12,107
Gross Unrealized Gains 16 0
Gross Unrealized Losses (9) (85)
Fair Value 10,950 12,022
Long-term marketable securities [Member] | Corporate debt securities [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost 16,799 17,219
Gross Unrealized Gains 289 5
Gross Unrealized Losses (155) (519)
Fair Value 16,933 16,705
Long-term marketable securities [Member] | Asset-backed securities and other [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost 10,752 10,649
Gross Unrealized Gains 55 0
Gross Unrealized Losses (116) (152)
Fair Value $ 10,691 $ 10,497