Fair Value of Financial Instruments - Summary of Changes in the Fair Value of the Company's Preferred Stock Warrant Liability (Detail) $ in Thousands	6 Months Ended
	Jun. 30, 2015 USD ($)
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance, January 1, 2015	$ 3,219
Fair Value, Inputs, Level 3 [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance, January 1, 2015	3,219
Change in fair value	3,123
Ending balance, June 30, 2015	$ 96