Cash, Cash Equivalents, and Short-Term Investments - Schedule of Short-Term Investments at Fair Value and Length of Continuous Unrealized Loss Position (Detail) - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015
Schedule Of Available For Sale Securities [Line Items]
Less than 12 Months, Fair Value	$ 49,463	$ 73,673
Less than 12 Months, Unrealized Losses	58	286
12 Months or Greater, Fair Value	13,116	10,609
12 Months or Greater, Unrealized Losses	9	14
Total, Fair Value	62,579	84,282
Total, Unrealized Losses	67	300
Commercial Paper [Member]
Schedule Of Available For Sale Securities [Line Items]
Less than 12 Months, Fair Value	11,548
Less than 12 Months, Unrealized Losses	0
12 Months or Greater, Fair Value	0
12 Months or Greater, Unrealized Losses	0
Total, Fair Value	11,548
Total, Unrealized Losses	0
Corporate Debt Obligations [Member]
Schedule Of Available For Sale Securities [Line Items]
Less than 12 Months, Fair Value	33,916	73,673
Less than 12 Months, Unrealized Losses	55	286
12 Months or Greater, Fair Value	13,116	10,609
12 Months or Greater, Unrealized Losses	9	14
Total, Fair Value	47,032	84,282
Total, Unrealized Losses	64	$ 300
US Government Agencies [Member]
Schedule Of Available For Sale Securities [Line Items]
Less than 12 Months, Fair Value	3,999
Less than 12 Months, Unrealized Losses	3
12 Months or Greater, Fair Value	0
12 Months or Greater, Unrealized Losses	0
Total, Fair Value	3,999
Total, Unrealized Losses	$ 3