Description of Business, Basis of Presentation and Summary of Significant Accounting Policies - Net (Loss) Income per Share (Details) - USD ($)	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Numerator:
Net income (loss)	$ 4,293,390	$ 1,297,931	$ (235,272)	$ (4,212,661)	$ (68,116,890)	$ 2,222,722	$ 856,595	$ 445,846	$ 1,143,388	$ (64,591,727)	$ 46,268,618
Denominator:
Weighted-average shares outstanding (in shares)									73,085,542	68,743,956	51,963,702
Effect of dilutive securities (in shares)									2,530,897	0	5,781,950
Weighted-average shares outstanding - diluted (in shares)									75,616,439	68,743,956	57,745,652
Basic income (loss) per share (in dollars per share)	$ 0.06	$ 0.02	$ 0.00	$ (0.06)	$ (0.95)	$ 0.03	$ 0.01	$ 0.01	$ 0.02	$ (0.94)	$ 0.89
Diluted income (loss) per share (in dollars per share)	$ 0.06	$ 0.02	$ 0.00	$ (0.06)	$ (0.95)	$ 0.03	$ 0.01	$ 0.01	$ 0.02	$ (0.94)	$ 0.80