Fair Value of Financial Instruments - Schedule of Assets and Liabilities Measured at Fair Value on a Recurring Basis (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Assets:
Investments	$ 57,279
Commercial Paper [Member]
Assets:
Investments	26,796
Corporate Debt Securities [Member]
Assets:
Investments	30,483
Level 1 [Member] | Recurring Basis [Member] | Money Market Funds [Member]
Assets:
Cash equivalents	59,471	47,740
Level 1 [Member] | Recurring Basis [Member] | Commercial Paper [Member]
Assets:
Cash equivalents
Investments
Level 1 [Member] | Recurring Basis [Member] | Corporate Debt Securities [Member]
Assets:
Investments
Level 2 [Member] | Recurring Basis [Member] | Money Market Funds [Member]
Assets:
Cash equivalents
Level 2 [Member] | Recurring Basis [Member] | Commercial Paper [Member]
Assets:
Cash equivalents		13,998
Investments	26,796	49,680
Level 2 [Member] | Recurring Basis [Member] | Corporate Debt Securities [Member]
Assets:
Investments	30,483	40,436
Level 3 [Member] | Recurring Basis [Member] | Money Market Funds [Member]
Assets:
Cash equivalents
Level 3 [Member] | Recurring Basis [Member] | Commercial Paper [Member]
Assets:
Cash equivalents
Investments
Level 3 [Member] | Recurring Basis [Member] | Corporate Debt Securities [Member]
Assets:
Investments