Summary of Significant Accounting Policies - Assets and Liabilities Measured at Fair Value on a Recurring Basis (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Liabilities
Expected volatility rate period	180 days
Maximum [Member]
Liabilities
Volatility rate	40.00%
Fair Value, Measurements, Recurring [Member] | Common Stock Warrant Liabilities [Member]
Liabilities
Liabilities measured at fair value on a recurring basis	$ 809	$ 6,196
Fair Value, Measurements, Recurring [Member] | Contingent Purchase Consideration [Member]
Liabilities
Liabilities measured at fair value on a recurring basis	52,800
Fair Value, Measurements, Recurring [Member] | Embedded Derivative Liabilities [Member]
Liabilities
Liabilities measured at fair value on a recurring basis		51,000
Fair Value, Measurements, Recurring [Member] | Money market fund shares [Member]
Assets
Assets measured at fair value on a recurring basis	87,792	148,588
Fair Value, Measurements, Recurring [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Common Stock Warrant Liabilities [Member]
Liabilities
Liabilities measured at fair value on a recurring basis	0	0
Fair Value, Measurements, Recurring [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Contingent Purchase Consideration [Member]
Liabilities
Liabilities measured at fair value on a recurring basis	0
Fair Value, Measurements, Recurring [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Embedded Derivative Liabilities [Member]
Liabilities
Liabilities measured at fair value on a recurring basis		0
Fair Value, Measurements, Recurring [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Money market fund shares [Member]
Assets
Assets measured at fair value on a recurring basis	87,792	148,588
Fair Value, Measurements, Recurring [Member] | Significant Other Observable Inputs (Level 2) [Member] | Common Stock Warrant Liabilities [Member]
Liabilities
Liabilities measured at fair value on a recurring basis	0	0
Fair Value, Measurements, Recurring [Member] | Significant Other Observable Inputs (Level 2) [Member] | Contingent Purchase Consideration [Member]
Liabilities
Liabilities measured at fair value on a recurring basis	0
Fair Value, Measurements, Recurring [Member] | Significant Other Observable Inputs (Level 2) [Member] | Embedded Derivative Liabilities [Member]
Liabilities
Liabilities measured at fair value on a recurring basis		0
Fair Value, Measurements, Recurring [Member] | Significant Other Observable Inputs (Level 2) [Member] | Money market fund shares [Member]
Assets
Assets measured at fair value on a recurring basis	0	0
Fair Value, Measurements, Recurring [Member] | Significant Unobservable Inputs (Level 3) [Member] | Common Stock Warrant Liabilities [Member]
Liabilities
Liabilities measured at fair value on a recurring basis	809	6,196
Fair Value, Measurements, Recurring [Member] | Significant Unobservable Inputs (Level 3) [Member] | Contingent Purchase Consideration [Member]
Liabilities
Liabilities measured at fair value on a recurring basis	52,800
Fair Value, Measurements, Recurring [Member] | Significant Unobservable Inputs (Level 3) [Member] | Embedded Derivative Liabilities [Member]
Liabilities
Liabilities measured at fair value on a recurring basis		51,000
Fair Value, Measurements, Recurring [Member] | Significant Unobservable Inputs (Level 3) [Member] | Money market fund shares [Member]
Assets
Assets measured at fair value on a recurring basis	$ 0	$ 0