Stock Option Plan (Details 3) - USD ($)	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Intrinsic Value
Intrinsic value of options exercised	$ 1,382,255	$ 0	$ 275,492
Tax benefits recognized	$ 0
Stock options
Stock Options
Weighted average grant date fair value (in dollars per share)	$ 4.60	$ 3.16	$ 4.54
Unrecognized compensation cost
Unrecognized compensation cost	$ 10,430,604	$ 4,862,030
Weighted-average remaining vesting period for recognition	3 years 1 month 6 days	3 years
Weighted-average assumptions
Dividend yield	0.00%	0.00%	0.00%
Expected volatility (weighted-average)	75.00%	85.00%	91.00%
Expected term (in years)	6 years 16 days	5 years 9 months 18 days	5 years
Number of Options
Balance outstanding	4,913,472	4,287,545	3,711,303
Granted (in shares)	2,688,500	1,410,038	1,144,760
Exercised (in shares)	(265,166)		(52,500)
Forfeited (in shares)	(388,176)	(784,111)	(516,018)
Balance outstanding	6,948,630	4,913,472	4,287,545	3,711,303
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Number	2,825,398
Weighted-Average Exercise Price Per Share
Balance outstanding at the beginning of the period (in dollars per share)	$ 4.66	$ 5.18	$ 4.69
Granted (in dollars per share)	7.02	4.42	6.33
Exercised (in dollars per share)	3.25		4.30
Forfeited (in dollars per share)	7.75	7.08	4.35
Balance outstanding at the end of the period (in dollars per share)	5.45	$ 4.66	$ 5.18	$ 4.69
Vested and exercisable at the end of the period (in dollars per share)	$ 4.38
Intrinsic Value
Intrinsic value of options outstanding	$ 5,903,466	$ 2,808,083	$ 5,896,329	$ 8,301,484
Vested and Exercisable at the end of the period, Intrinsic Value	$ 4,194,205
Weighted Average Remaining Contractual Life	7 years 9 months 11 days	7 years 7 months 6 days	6 years 8 months 12 days	6 years 3 months 18 days
Weighted average life vested and exercisable	6 years 17 days
Stock options | Minimum
Weighted-average assumptions
Risk-free interest rate	1.35%	1.42%	0.74%
Expected volatility (range)	73.00%	81.00%	82.00%
Stock options | Maximum
Weighted-average assumptions
Risk-free interest rate	2.15%	2.10%	1.50%
Expected volatility (range)	77.00%	86.00%	100.00%