Summary of Significant Accounting Policies - Assets and Liabilities Measured at Fair Value on a Recurring Basis (Detail) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Common Stock Warrant Liabilities
Liabilities
Liabilities measured at fair value on a recurring basis	$ 222	$ 809
Contingent Consideration Liabilities
Liabilities
Liabilities measured at fair value on a recurring basis	53,400	52,800
Money market fund shares
Assets
Assets measured at fair value on a recurring basis	75,386	87,792
Quoted Prices in Active Markets for Identical Assets (Level 1) | Common Stock Warrant Liabilities
Liabilities
Liabilities measured at fair value on a recurring basis	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Contingent Consideration Liabilities
Liabilities
Liabilities measured at fair value on a recurring basis	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Money market fund shares
Assets
Assets measured at fair value on a recurring basis	75,386	87,792
Significant Other Observable Inputs (Level 2) | Common Stock Warrant Liabilities
Liabilities
Liabilities measured at fair value on a recurring basis	0	0
Significant Other Observable Inputs (Level 2) | Contingent Consideration Liabilities
Liabilities
Liabilities measured at fair value on a recurring basis	0	0
Significant Other Observable Inputs (Level 2) | Money market fund shares
Assets
Assets measured at fair value on a recurring basis	0	0
Significant Unobservable Inputs (Level 3) | Common Stock Warrant Liabilities
Liabilities
Liabilities measured at fair value on a recurring basis	222	809
Significant Unobservable Inputs (Level 3) | Contingent Consideration Liabilities
Liabilities
Liabilities measured at fair value on a recurring basis	53,400	52,800
Significant Unobservable Inputs (Level 3) | Money market fund shares
Assets
Assets measured at fair value on a recurring basis	$ 0	$ 0