Stockholders' Equity - Stock Option Activity (Details) - USD ($)	3 Months Ended			9 Months Ended
	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Sep. 30, 2018
Equity [Abstract]
Unrecognized compensation cost, net of forfeitures	$ 4,900,000			$ 4,900,000
Weighted average period to recognize stock compensation expense				1 year 8 months 12 days
Options
Outstanding, Beginning Balance	5,720,507	5,996,771	5,878,660	5,878,660
Granted during period	48,700	242,400	688,192
Exercised during period	(442,913)	(512,795)	(561,088)
Expired during period			(8,993)
Forfeited during period	(16,950)	(5,869)
Outstanding, Ending Balance	5,309,344	5,720,507	5,996,771	5,309,344
Weighted-Average Exercise Price
Outstanding, Beginning Balance	$ 5.79	$ 5.78	$ 5.93	$ 5.93
Granted during period	16.74	10.86	3.07
Exercised during period	7.57	8.16	4.10
Expired during period			3.06
Forfeited during period	4.77	2.82
Outstanding, Ending Balance	$ 5.74	$ 5.79	$ 5.78	$ 5.74
Additional disclosures
Options, Exercisable	3,550,137	3,970,287	4,290,445	3,550,137
Weighted Average Exercise Price, Exercisable	$ 6.42	$ 6.56	$ 6.92	$ 6.42
Weighted Average Remaining Contractual Term	6 years 1 month 21 days	6 years 3 months 11 days	6 years 2 months 5 days
Weighted Average Remaining Contractual Term exercisable at end of period	4 years 10 months 2 days	5 years 1 month 2 days	5 years 7 days
Aggregate Intrinsic Value	$ 63,541,222	$ 45,908,925	$ 22,125,418	$ 63,541,222
Aggregate Intrinsic Value, exercisable at end of period	$ 40,064,166	$ 28,812,888	$ 11,551,954	$ 40,064,166