Stockholders' Equity - Summary of Option Activity (Details) - $ / shares	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Number of Options
Outstanding at beginning of period (in shares)	292,871	248,512	530,734
Granted (in shares)	689,300	100,746	192,984
Canceled (in shares)	(177,493)	(46,387)	(377,095)
Expired (in shares)	(27,525)	(10,000)	(56,111)
Exercised (in shares)	0		(42,000)
Outstanding at end of period (in shares)	777,153	292,871	248,512
Vested and expected to vest (in shares)	578,486
Exercisable (in shares)	111,595
Weighted Average Exercise Price Per Share
Outstanding at beginning of period (in dollars per share)	$ 3.78	$ 5.76	$ 7.48
Granted (in dollars per share)	0.44	1.97	3.55
Canceled (in dollars per share)	2.55	6.96	6.71
Expired (in dollars per share)	5.33	20.00	10.65
Exercised (in dollars per share)			2.30
Outstanding at end of period (in dollars per share)	1.04	$ 3.78	$ 5.76
Vested and expected to vest (in dollars per share)	1.25
Exercisable (in dollars per share)	$ 4.61

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.