Marketable Securities - Schedule of Available-For-Sale Securities, All of Which Have Maturities of Twelve Months or Less (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2013
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 90,140
Unrealized Gains
Unrealized Losses	(24)
Fair Value	90,116
Commercial Paper [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	49,685
Unrealized Gains
Unrealized Losses	(5)
Fair Value	49,680
Corporate Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	40,455
Unrealized Gains
Unrealized Losses	(19)
Fair Value	$ 40,436