Stock-Based Compensation - Summary of Stock-Based Compensation Activity (Detail) - 2005 Plan, 2008 Plan and 2015 Plan [Member] - USD ($)	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Non-Vested Stock, Number of Shares Outstanding
Number of Shares Outstanding, Beginning balance			404
Number of Shares Outstanding, Non-vested stock granted			35,353
Number of Shares Outstanding, Non-vested stock vested			(35,757)
Non-Vested Stock, Number of Shares Outstanding, Ending balance				404
Non-Vested Stock, Weighted-Average Grant Date Fair Value Per Share
Weighted-Average Grant Date Fair Value Per Share, Beginning balance			$ 0.3
Weighted-Average Grant Date Fair Value Per Share, Non-vested stock granted			0.29
Weighted-Average Grant Date Fair Value Per Share, Non-vested stock vested			$ 0.29
Weighted-Average Grant Date Fair Value Per Share, Ending balance				$ 0.3
Options Outstanding, Shares Available for Grant
Shares Available for Grant, Beginning balance	1,550,101	637,768	555,135
Shares Available for Grant, Awards authorized	3,400,000	3,221,477	520,134
Shares Available for Grant, Granted	(1,471,664)	(2,309,681)	(403,759)
Non-vested stock granted			(35,353)
Shares Available for Grant, Exercised	0	0	0
Shares Available for Grant, Cancelled	45,442	537	1,611
Shares Available for Grant, Ending balance	3,523,879	1,550,101	637,768	555,135
Options Outstanding, Number of Shares Outstanding
Number of Shares Outstanding, Beginning balance	2,138,096	582,152	271,276
Number of Shares Outstanding, Options granted	1,471,664	2,309,681	403,759
Number of Shares Outstanding, Options exercised	(41,505)	(752,698)	(91,272)
Number of Shares Outstanding, Options cancelled	(45,442)	(1,039)	(1,611)
Number of Shares Outstanding, Ending balance	3,522,813	2,138,096	582,152	271,276
Number of Shares Outstanding, Exercisable	2,152,742
Number of Shares Outstanding, Vested and expected to vest	3,417,287
Options Outstanding, Weighted-Average Exercise Price Per Share
Weighted-Average Exercise Price Per Share, Beginning balance	$ 0.91	$ 0.37	$ 0.32
Weighted-Average Exercise Price Per Share, Options granted	8.06	0.93	0.37
Weighted-Average Exercise Price Per Share, Options exercised	0.76	0.54	0.27
Weighted-Average Exercise Price Per Share, Options cancelled	7.76	2.08	0.26
Weighted-Average Exercise Price Per Share, Ending balance	3.81	$ 0.91	$ 0.37	$ 0.32
Weighted-Average Exercise Price Per Share, Exercisable	1.04
Weighted-Average Exercise Price Per Share, Vested and expected to vest	$ 3.74
Options Outstanding, Weighted-Average Remaining Contractual Term (Years)
Weighted-Average Remaining Contractual Term (Years)	8 years 8 months 23 days	9 years 3 months 15 days	8 years 7 months 17 days	7 years 7 months 28 days
Weighted-Average Remaining Contractual Term (Year), Exercisable	8 years 4 months 6 days
Weighted-Average Remaining Contractual Term (Year), Vested and expected to vest	8 years 9 months 7 days
Options Outstanding, Aggregate Intrinsic Value of Outstanding Options
Aggregate Intrinsic Value of Outstanding Options	$ 40,425,000	$ 3,153,000	$ 48,000	$ 0
Aggregate Intrinsic Value of Outstanding Options, Exercisable	30,140,000
Aggregate Intrinsic Value of Outstanding Options, Vested and expected to vest	$ 39,437,000