Stockholders' Equity - Summary of Option Activity (Details) - $ / shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Number of Options
Outstanding at beginning of period (in shares)	530,734	602,207	459,271
Granted (in shares)	192,984	167,819	340,500
Canceled (in shares)	(377,095)	(160,126)	(147,152)
Exercised (in shares)	(42,000)	(79,166)	(50,412)
Outstanding at end of period (in shares)	248,512	530,734	602,207
Vested and expected to vest (in shares)	228,880
Exercisable (in shares)	110,476
Weighted Average Exercise Price Per Share
Outstanding at beginning of period (in dollars per share)	$ 7.48	$ 8.58	$ 8.95
Granted (in dollars per share)	3.55	7.31	8.65
Canceled (in dollars per share)	$ 6.71	12.94	10.10
Share-based Compensation Arrangement by Share-based Payment Award, Options, Forfeitures and Expirations in Period	56,111
Exercised (in dollars per share)	$ 2.30	4.48	4.69
Outstanding at end of period (in dollars per share)	5.76	$ 7.48	$ 8.58
Share-based Compensation Arrangements by Share-based Payment Award, Options, Expirations in Period, Weighted Average Exercise Price	10.65
Vested and expected to vest (in dollars per share)	5.97
Exercisable (in dollars per share)	$ 8.63