Summary of Significant Accounting Policies - Revenue and Deferred Revenue (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2018	Dec. 31, 2016
Deferred revenue
Deferred Revenue	$ 3,999,452	$ 4,204,647	$ 4,228,300
ASU 2014-09
Accounting Policies [Line Items]
Revenue recognized	$ 3,167,000