Stock-Based Compensation - Summary of Stock Option Transactions (Details) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2018 USD ($) $ / shares shares
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Number of shares outstanding, beginning balance (in shares) | shares	2,979,285
Number of shares, options granted (in shares) | shares	1,640,589
Number of shares, options exercised (in shares) | shares	(45,805)
Number of shares, options canceled (in shares) | shares	(1,214,021)
Number of shares outstanding, ending balance (in shares) | shares	3,360,048
Number of shares, vested and expected to vest at end of period (in shares) | shares	3,174,081
Number of shares, vested and exercisable at period end (in shares) | shares	1,634,506
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Abstract]
Weighted average exercise price outstanding, beginning balance (in dollars per share) | $ / shares	$ 6.49
Weighted average exercise price, options granted (in dollars per share) | $ / shares	4.78
Weighted average exercise price, options exercised (in dollars per share) | $ / shares	1.16
Weighted average exercise price, options canceled (in dollars per share) | $ / shares	6.22
Weighted average exercise price outstanding, ending balance (in dollars per share) | $ / shares	5.83
Weighted average exercise price, vested and expected to vest (in dollars per share) | $ / shares	5.81
Weighted average exercise price, vested and exercisable (in dollars per share) | $ / shares	$ 5.99
Weighted average contractual life outstanding, ending balance	8 years
Weighted average contractual life, vested and expected to vest	7 years 12 months
Weighted average contractual life, vested and exercisable	7 years 2 months
Aggregate intrinsic value outstanding | $	$ 535
Aggregate intrinsic value, vested and expected to vest | $	531
Aggregate intrinsic value, vested and exercisable | $	$ 483