Stockholders' Equity Common Stock - Summary of Stock Option Activity (Detail) - USD ($) $ / shares in Units, $ in Thousands	6 Months Ended	12 Months Ended
	Jun. 30, 2017	Dec. 31, 2016
Equity [Abstract]
Number of Shares, Beginning Balance	5,069,133
Number of Shares, Granted	1,609,500
Number of Shares, Exercised	(56,282)
Number of Shares, Forfeited	(307,513)
Number of Shares, Ending Balance	6,314,838	5,069,133
Number of Shares, Options exercisable	2,800,162
Weighted Average Exercise Price, Beginning Balance	$ 14.36
Weighted Average Exercise Price, Granted	10.07
Weighted Average Exercise Price, Exercised	0.65
Weighted Average Exercise Price, Forfeited	20.18
Weighted Average Exercise Price, Ending Balance	13.11	$ 14.36
Weighted Average Exercise Price, Options exercisable	$ 11.10
Weighted Average Remaining Contractual Term, Outstanding	8 years 1 month 24 days	8 years 3 months 4 days
Weighted Average Remaining Contractual Term, Options exercisable	7 years 4 months 2 days
Aggregate Intrinsic Value, Outstanding	$ 20,875	$ 16,736
Aggregate Intrinsic Value, Options exercisable	$ 14,634