Stockholders' Equity - Stock Option Activity (Details) - USD ($)	6 Months Ended	12 Months Ended
	Jun. 30, 2018	Dec. 31, 2017
Number of Stock Options
Exercised (in shares)	(131,051)	(2,080,648)
2012 Omnibus Incentive Plan
Number of Stock Options
Outstanding (in shares)	3,724,892
Options granted (in shares)	0
Exercised (in shares)	(131,051)
Forfeited or expired (in shares)	(95,867)
Outstanding (in shares)	3,497,974	3,724,892
Exercisable (in shares)	2,695,101
Weighted-Average Exercise Price
Outstanding, Weighted-Average Exercise Price (in dollars per share)	$ 3.07
Granted, Weighted-Average Exercise Price (in dollars per share)	0.00
Exercised, Weighted-Average Exercise Price (in dollars per share)	1.77
Forfeited or expired, Weighted-Average Exercise Price (in dollars per share)	3.49
Outstanding, Weighted-Average Exercise Price (in dollars per share)	3.11	$ 3.07
Exercisable, Weighted-Average Exercise Price (in dollars per share)	$ 2.75
Outstanding, Weighted-Average Remaining Contractual Life	7 years 3 months 18 days
Exercisable, Weighted-Average Remaining Contractual Life	6 years 10 months 24 days
Outstanding, Aggregate Intrinsic Value	$ 5,301,183
Exercisable, Aggregate Intrinsic Value	$ 4,895,933
2006 Stock Plan
Number of Stock Options
Outstanding (in shares)	1,194,081
Options granted (in shares)	0
Exercised (in shares)	0
Forfeited or expired (in shares)	(96,000)
Outstanding (in shares)	1,098,081	1,194,081
Exercisable (in shares)	1,053,902
Weighted-Average Exercise Price
Outstanding, Weighted-Average Exercise Price (in dollars per share)	$ 4.08
Granted, Weighted-Average Exercise Price (in dollars per share)	0.00
Exercised, Weighted-Average Exercise Price (in dollars per share)	0.00
Forfeited or expired, Weighted-Average Exercise Price (in dollars per share)	5.06
Outstanding, Weighted-Average Exercise Price (in dollars per share)	3.99	$ 4.08
Exercisable, Weighted-Average Exercise Price (in dollars per share)	$ 4.00
Outstanding, Weighted-Average Remaining Contractual Life	3 years 3 months 18 days
Exercisable, Weighted-Average Remaining Contractual Life	3 years 4 months 24 days
Outstanding, Aggregate Intrinsic Value	$ 564,307
Exercisable, Aggregate Intrinsic Value	$ 529,848
The Amended and Restated 2016 Inducement Omnibus Incentive Plan
Number of Stock Options
Outstanding (in shares)	734,168
Options granted (in shares)	0
Exercised (in shares)	0
Forfeited or expired (in shares)	(248,332)
Outstanding (in shares)	485,836	734,168
Exercisable (in shares)	272,502
Weighted-Average Exercise Price
Outstanding, Weighted-Average Exercise Price (in dollars per share)	$ 5.18
Granted, Weighted-Average Exercise Price (in dollars per share)	0.00
Exercised, Weighted-Average Exercise Price (in dollars per share)	0.00
Forfeited or expired, Weighted-Average Exercise Price (in dollars per share)	5.16
Outstanding, Weighted-Average Exercise Price (in dollars per share)	5.19	$ 5.18
Exercisable, Weighted-Average Exercise Price (in dollars per share)	$ 5.27
Outstanding, Weighted-Average Remaining Contractual Life	8 years 7 months 6 days
Exercisable, Weighted-Average Remaining Contractual Life	8 years 7 months 6 days
Outstanding, Aggregate Intrinsic Value	$ 0
Exercisable, Aggregate Intrinsic Value	$ 0