Short-Term Investments - Short-Term Investments Available-for-Sale Securities (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	$ 48,695	$ 32,693
Gross unrealized gains	8	25
Gross unrealized losses	(29)	(3)
Fair value	48,674	32,715
U.S. government-related debt securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	1,518	1,565
Gross unrealized gains	1	1
Gross unrealized losses	0	0
Fair value	1,519	1,566
Corporate debt securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	43,877	31,128
Gross unrealized gains	7	24
Gross unrealized losses	(27)	(3)
Fair value	43,857	31,149
Asset-backed securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	3,300
Gross unrealized gains	0
Gross unrealized losses	(2)
Fair value	$ 3,298