Fair Value of Financial Instruments - Assets and Liabilities Measured at Fair Value on a Recurring Basis (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Assets:
Total assets at fair value	$ 59,862	$ 30,325
Liabilities:
Total liabilities at fair value	1	19
Warrant Liability [Member]
Liabilities:
Total liabilities at fair value	1	19
Money Market Funds [Member]
Assets:
Total assets at fair value	59,862	30,325
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Assets:
Total assets at fair value	59,862	30,325
Liabilities:
Total liabilities at fair value
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Warrant Liability [Member]
Liabilities:
Total liabilities at fair value
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Money Market Funds [Member]
Assets:
Total assets at fair value	59,862	30,325
Significant Other Observable Inputs (Level 2) [Member]
Assets:
Total assets at fair value
Liabilities:
Total liabilities at fair value
Significant Other Observable Inputs (Level 2) [Member] | Warrant Liability [Member]
Liabilities:
Total liabilities at fair value
Significant Other Observable Inputs (Level 2) [Member] | Money Market Funds [Member]
Assets:
Total assets at fair value
Significant Unobservable Inputs (Level 3) [Member]
Assets:
Total assets at fair value
Liabilities:
Total liabilities at fair value	1	19
Significant Unobservable Inputs (Level 3) [Member] | Warrant Liability [Member]
Liabilities:
Total liabilities at fair value	1	19
Significant Unobservable Inputs (Level 3) [Member] | Money Market Funds [Member]
Assets:
Total assets at fair value