Summary of Significant Accounting Policies - Assets and Liabilities Measured at Fair Value on a Recurring Basis (Detail) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2015	Dec. 31, 2014
Liabilities
Expected volatility rate period	180 days
Minimum
Liabilities
Maximum volatility rate	40.00%
Common Stock Warrant Liabilities
Liabilities
Liabilities measured at fair value on a recurring basis	$ 5,657	$ 5,093
Contingent Purchase Consideration
Liabilities
Liabilities measured at fair value on a recurring basis	51,400	53,000
Money market fund shares
Assets
Assets measured at fair value on a recurring basis	69,208	8,021
Short-term investments
Assets
Assets measured at fair value on a recurring basis	9,062
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 Purchase Consideration
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	69,208	8,021
Quoted Prices in Active Markets for Identical Assets (Level 1) | Short-term investments
Assets
Assets measured at fair value on a recurring basis	0
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 Purchase Consideration
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 Other Observable Inputs (Level 2) | Short-term investments
Assets
Assets measured at fair value on a recurring basis	0
Significant Unobservable Inputs (Level 3) | Common Stock Warrant Liabilities
Liabilities
Liabilities measured at fair value on a recurring basis	5,657	5,093
Significant Unobservable Inputs (Level 3) | Contingent Purchase Consideration
Liabilities
Liabilities measured at fair value on a recurring basis	51,400	53,000
Significant Unobservable Inputs (Level 3) | Money market fund shares
Assets
Assets measured at fair value on a recurring basis	0	$ 0
Significant Unobservable Inputs (Level 3) | Short-term investments
Assets
Assets measured at fair value on a recurring basis	$ 9,062