Short-term Investments - Summary of Available-for-Sale Securities (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Schedule of Available-for-sale Securities [Line Items]
Total available-for-sale securities, Amortized cost	$ 32,917
Total available-for-sale securities, Gross unrealized gains	13
Total available-for-sale securities, Gross unrealized losses	(8)
Total available-for-sale securities, Fair value	32,922
U.S. government-related debt securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Total available-for-sale securities, Amortized cost	1,581
Total available-for-sale securities, Gross unrealized gains	2
Total available-for-sale securities, Fair value	1,583
Corporate debt securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Total available-for-sale securities, Amortized cost	31,336
Total available-for-sale securities, Gross unrealized gains	11
Total available-for-sale securities, Gross unrealized losses	(8)
Total available-for-sale securities, Fair value	$ 31,339