Cash, Cash Equivalents and Short-Term Investments - Schedule of Short-Term Investments at Fair Value and Length of Continuous Unrealized Loss Position (Detail) (Corporate Debt Obligations [Member], USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Corporate Debt Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	$ 12,735	$ 8,394
Less than 12 Months, Unrealized Losses	47	14
12 Months or Greater, Fair Value	12,088	0
12 Months or Greater, Unrealized Losses	6	0
Total, Fair Value	24,823	8,394
Total, Unrealized Losses	$ 53	$ 14