Short-Term Investments - Short-Term Investments Available-for-Sale Securities (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	$ 58,396	$ 32,693
Gross unrealized gains	17	25
Gross unrealized losses	(10)	(3)
Fair value	58,403	32,715
U.S. government-related debt securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	1,534	1,565
Gross unrealized gains	1	1
Gross unrealized losses
Fair value	1,535	1,566
Corporate debt securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	53,562	31,128
Gross unrealized gains	15	24
Gross unrealized losses	(9)	(3)
Fair value	53,568	31,149
Asset-backed securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	3,300
Gross unrealized gains	1
Gross unrealized losses	(1)
Fair value	$ 3,300