Fair Value of Financial Instruments - Company's Available-for-sale Securities by Level within Fair Value Hierarchy (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Assets at fair value	$ 41,169
Money Market Fund [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Assets at fair value	8,454	20,510
Short-term Investments [Member] | U.S. Government-related Debt Securities [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Assets at fair value	1,566
Short-term Investments [Member] | Corporate Debt Securities [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Assets at fair value	31,149
Level 1 [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Assets at fair value	8,454
Level 1 [Member] | Money Market Fund [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Assets at fair value	8,454	20,510
Level 2 [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Assets at fair value	32,715
Level 2 [Member] | Money Market Fund [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Assets at fair value
Level 2 [Member] | Short-term Investments [Member] | U.S. Government-related Debt Securities [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Assets at fair value	1,566
Level 2 [Member] | Short-term Investments [Member] | Corporate Debt Securities [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Assets at fair value	31,149
Level 3 [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Assets at fair value
Level 3 [Member] | Money Market Fund [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Assets at fair value
Level 3 [Member] | Short-term Investments [Member] | U.S. Government-related Debt Securities [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Assets at fair value
Level 3 [Member] | Short-term Investments [Member] | Corporate Debt Securities [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Assets at fair value