Stockholders' Equity - Summary of Option Activity (Details) - $ / shares	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Number of Options
Outstanding at beginning of period (in shares)	248,512	530,734	602,207
Granted (in shares)	100,746	192,984	167,819
Canceled (in shares)	(46,387)	(377,095)	(160,126)
Exercised (in shares)	0	(42,000)	(79,166)
Outstanding at end of period (in shares)	292,871	248,512	530,734
Vested and expected to vest (in shares)	272,247
Exercisable (in shares)	159,007
Weighted Average Exercise Price Per Share
Outstanding at beginning of period (in dollars per share)	$ 5.76	$ 7.48	$ 8.58
Granted (in dollars per share)	1.97	3.55	7.31
Canceled (in dollars per share)	$ 6.96	$ 6.71	12.94
Share-based Compensation Arrangement by Share-based Payment Award, Options, Forfeitures and Expirations in Period	(10,000)	(56,111)
Exercised (in dollars per share)		$ 2.30	4.48
Outstanding at end of period (in dollars per share)	$ 3.78	5.76	$ 7.48
Share-based Compensation Arrangements by Share-based Payment Award, Options, Expirations in Period, Weighted Average Exercise Price	20.00	$ 10.65
Vested and expected to vest (in dollars per share)	3.90
Exercisable (in dollars per share)	$ 4.98

The number of shares into which fully or partially vested stock options outstanding as of the balance sheet date can be currently converted under the option plan.

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- Definition

The weighted-average price as of the balance sheet date at which grantees can acquire the shares reserved for issuance on vested portions of options outstanding and currently exercisable under the stock option plan.