Share/Stock-Based Compensation - Summary of Employee and Nonemployee Stock Option Activity (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Mar. 10, 2015
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Shares Issuable Under Options, Outstanding	1,146,935
Shares Issuable Under Options, Granted	1,971,300
Shares Issuable Under Options, Exercised	(200,600)
Shares Issuable Under Options, Forfeited	(556,275)
Shares Issuable Under Options, Outstanding	2,361,360	1,146,935
Shares Issuable Under Options, Options vested and expected to vest	2,351,832		100,446
Shares Issuable Under Options, Options exercisable	565,920
Weighted Average Exercise Price, Outstanding	$ 5.64
Weighted Average Exercise Price, Granted	5.22
Weighted Average Exercise Price, Exercised	3.50
Weighted Average Exercise Price, Forfeited	6.76
Weighted Average Exercise Price, Outstanding	5.21	$ 5.64
Weighted Average Exercise Price, Options vested and expected to vest	5.22
Weighted Average Exercise Price, Options exercisable	$ 6.47
Weighted Average Remaining Contractual Term, Outstanding	8 years 8 months 19 days	8 years 7 months 20 days
Weighted Average Remaining Contractual Term, Options vested and expected to vest	8 years 8 months 19 days
Weighted Average Remaining Contractual Term, Options exercisable	6 years 9 months 18 days
Aggregate Intrinsic Value, Outstanding	$ 2,482	$ 440
Aggregate Intrinsic Value, Options vested and expected to vest	2,464
Aggregate Intrinsic Value, Options exercisable	$ 318