Fair Value Measurements - Schedule of Short-Term Investments (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Schedule of Available-for-sale Securities [Line Items]
Short-term Investments, Amortized Cost	$ 52,973	$ 56,966
Short-term Investments, Gross Unrealized Holding Gains	16	10
Short-term Investments, Gross Unrealized Holding Losses	0	0
Short-term Investments, Fair Value	52,989	56,976
U.S. Treasury Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Short-term Investments, Amortized Cost	52,973	56,966
Short-term Investments, Gross Unrealized Holding Gains	16	10
Short-term Investments, Gross Unrealized Holding Losses	0	0
Short-term Investments, Fair Value	$ 52,989	$ 56,976