Stockholders' Equity - stock option activity (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Mar. 31, 2016	Jun. 30, 2016
Equity [Abstract]
Options, Outstanding, Beginning Balance	6,479,347	5,686,815	5,686,815
Options, Granted during period	189,900	845,247
Options, Exercised during period	(7,538)	(48,879)
Options, Expired during period		(3,836)
Options, Forfeited during period	(105,940)
Options, Outstanding, Ending Balance	6,555,769	6,479,347	6,555,769
Options, Exercisable	4,637,674	4,171,230	4,637,674
Weighted Average Exercise Price, Outstanding, Beginning Balance	$ 6.43	$ 6.87	$ 6.87
Weighted Average Exercise Price, Granted during period	3.45	3.18
Weighted Average Exercise Price, Exercised during period	2.10	1.91
Weighted Average Exercise Price, Expired during period		7.34
Weighted Average Exercise Price, Forfeited during period	3.94
Weighted Average Exercise Price, Outstanding, Ending Balance	6.38	6.43	6.38
Weighted Average Exercise Price, Exercisable	$ 6.65	$ 6.62	$ 6.65
Weighted Average Remaining Contractual Term, Outstanding, Ending Balance	6 years 7 months 6 days	6 years 9 months 15 days
Weighted Average Remaining Contractual Term, Exercisable	5 years 8 months 12 days	5 years 7 months 21 days
Aggregate Intrinsic Value, Outstanding, Ending Balance	$ 392,534	$ 308,641	$ 392,534
Aggregate Intrinsic Value, Exercisable	$ 372,270	$ 308,641	$ 372,270