Short-term Investments - Summary of Investments in Continuous Unrealized Loss Position for Less Than 12 Months (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015
Schedule of Available-for-sale Securities [Line Items]
Less Than 12 Months, Fair value	$ 30,758
Less Than 12 Months, Gross unrealized losses	(18)
12 Months or Greater, Fair value	1,999
12 Months or Greater, Gross unrealized losses	(1)
Total, Fair value	32,757
Total, Gross unrealized losses	(19)
Corporate debt securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Less Than 12 Months, Fair value	28,340
Less Than 12 Months, Gross unrealized losses	(17)
12 Months or Greater, Fair value	1,999
12 Months or Greater, Gross unrealized losses	(1)
Total, Fair value	30,339
Total, Gross unrealized losses	(18)
Asset-backed securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Less Than 12 Months, Fair value	2,418
Less Than 12 Months, Gross unrealized losses	(1)
12 Months or Greater, Fair value	0
12 Months or Greater, Gross unrealized losses	0
Total, Fair value	2,418
Total, Gross unrealized losses	$ (1)