Revenue - Disaggregation of Revenue (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
Disaggregation of Revenue [Line Items]
Revenue	$ 52,457,904	$ 45,716,053	$ 42,801,745	$ 37,637,793	$ 40,119,076	$ 32,246,472	$ 31,329,468	$ 20,058,797	$ 178,613,495	$ 123,753,813	$ 76,124,109
Revenue, as a percent									100.00%	100.00%	100.00%
User pay revenue
Disaggregation of Revenue [Line Items]
Revenue									$ 107,330,136	$ 33,791,592	$ 4,927,241
Revenue, as a percent									60.10%	27.30%	6.50%
Advertising
Disaggregation of Revenue [Line Items]
Revenue									$ 71,283,359	$ 89,962,221	$ 71,196,868
Revenue, as a percent									39.90%	72.70%	93.50%