Investments - Schedule of Fair Value of Available-for-Sale Investments by Type of Security (Detail) $ in Thousands	Dec. 31, 2015 USD ($)
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	$ 131,116
Gross Unrealized Gain	87
Gross Unrealized Loss	(54)
Fair Value	131,149
Commercial Paper [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	64,733
Gross Unrealized Gain	87
Fair Value	64,820
Corporate Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	46,538
Gross Unrealized Loss	(48)
Fair Value	46,490
Government Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	15,823
Gross Unrealized Loss	(4)
Fair Value	15,819
Treasury Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	4,022
Gross Unrealized Loss	(2)
Fair Value	$ 4,020