Fair Value of Financial Instruments - Company's Preferred Stock Warrant Liabilities by Level within Fair Value Hierarchy (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012
Fair Value Assets And Liabilities Components [Line Items]
Preferred stock warrant liability	$ 3,532
Level 1 [Member]
Fair Value Assets And Liabilities Components [Line Items]
Preferred stock warrant liability
Level 2 [Member]
Fair Value Assets And Liabilities Components [Line Items]
Preferred stock warrant liability
Level 3 [Member]
Fair Value Assets And Liabilities Components [Line Items]
Preferred stock warrant liability	$ 3,532