Stockholders' Equity - Stock Option Activity (Details) - USD ($)	6 Months Ended		12 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018
Number of Stock Options
Exercised (in shares)	(157,334)		(1,079,496)
2012 Omnibus Incentive Plan
Number of Stock Options
Outstanding (in shares)	2,447,315
Options granted (in shares)	0
Exercised (in shares)	(106,903)
Forfeited or expired (in shares)	(8,333)
Outstanding (in shares)	2,332,079		2,447,315
Exercisable (in shares)	2,028,441
Weighted- Average Exercise Price
Outstanding (in dollars per share)	$ 3.27
Granted (in dollars per share)	0.00
Exercised (in dollars per share)	4.33
Forfeited or expired (in dollars per share)	5.35
Outstanding (in dollars per share)	3.22		$ 3.27
Exercisable, Weighted-Average Exercise Price (in dollars per share)	$ 3.04
Outstanding, Weighted-Average Remaining Contractual Life	6 years 7 months 6 days
Exercisable, Weighted-Average Remaining Contractual Life	6 years 4 months 24 days
Outstanding, Aggregate Intrinsic Value	$ 1,714,956
Exercisable, Aggregate Intrinsic Value	$ 1,642,040
2006 Stock Plan
Number of Stock Options
Outstanding (in shares)	1,074,411
Options granted (in shares)	0
Exercised (in shares)	(23,764)
Forfeited or expired (in shares)	0
Outstanding (in shares)	1,050,647		1,074,411
Exercisable (in shares)	1,006,468
Weighted- Average Exercise Price
Outstanding (in dollars per share)	$ 4.00
Granted (in dollars per share)	0.00
Exercised (in dollars per share)	3.78
Forfeited or expired (in dollars per share)	0.00
Outstanding (in dollars per share)	4.00		$ 4.00
Exercisable, Weighted-Average Exercise Price (in dollars per share)	$ 4.02
Outstanding, Weighted-Average Remaining Contractual Life	2 years 4 months 6 days
Exercisable, Weighted-Average Remaining Contractual Life	2 years 4 months 6 days
Outstanding, Aggregate Intrinsic Value	$ 25,200
Exercisable, Aggregate Intrinsic Value	$ 25,200
The Amended and Restated 2016 Inducement Omnibus Incentive Plan
Number of Stock Options
Outstanding (in shares)	444,168
Options granted (in shares)	0
Exercised (in shares)	(26,667)	0
Forfeited or expired (in shares)	(97,501)
Outstanding (in shares)	320,000		444,168
Exercisable (in shares)	213,333
Weighted- Average Exercise Price
Outstanding (in dollars per share)	$ 5.10
Granted (in dollars per share)	0.00
Exercised (in dollars per share)	5.69
Forfeited or expired (in dollars per share)	5.02
Outstanding (in dollars per share)	5.07		$ 5.10
Exercisable, Weighted-Average Exercise Price (in dollars per share)	$ 5.07
Outstanding, Weighted-Average Remaining Contractual Life	7 years 7 months 6 days
Exercisable, Weighted-Average Remaining Contractual Life	7 years 7 months 6 days
Outstanding, Aggregate Intrinsic Value	$ 0
Exercisable, Aggregate Intrinsic Value	$ 0