Fair Value Measurements - Liabilities Measured at Fair Value on Recurring Basis (Detail) (USD $)	Dec. 31, 2012
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Total liabilities	$ 56,000
Preferred stock warrant liability [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Total liabilities	56,000
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Total liabilities	0
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Preferred stock warrant liability [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Total liabilities	0
Significant Other Observable Inputs (Level 2) [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Total liabilities	0
Significant Other Observable Inputs (Level 2) [Member] | Preferred stock warrant liability [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Total liabilities	0
Significant Unobservable Inputs (Level 3) [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Total liabilities	56,000
Significant Unobservable Inputs (Level 3) [Member] | Preferred stock warrant liability [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Total liabilities	$ 56,000