Preferred Stock Warrant Liability - Summary of Rollforward of Fair Value of Preferred Stock Warrant Liability (Detail) - USD ($)	3 Months Ended	9 Months Ended
	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Fair Value Inputs Quantitative Information [Abstract]
Balance as of December 31, 2014		$ 1,582,000
Loss on revaluation	$ 521,000	7,000	$ 504,000
Reclassification to stockholders’ equity		(1,589,000)
Balance as of September 30, 2015	$ 7,820	$ 17,260	$ 7,820