Fair Value Measurements - Summary of Changes in Estimated Fair Value of Preferred Stock Warrants Measured at Fair Value on Recurring Basis (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Fair Value Disclosures [Abstract]
Balance as of December 31, 2014			$ 1,810
Fair value of preferred stock warrants exercised	$ (18,200)		(19,253)
Change in fair value of preferred stock warrants	7,487	$ 503	17,443	$ 999
Balance as of September 30, 2015	$ 0		$ 0