Summary of Significant Accounting Policies - Income Taxes (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Taxes
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate		35.00%	35.00%	35.00%
Accounting Standards Update 2016-09 [Member]
Income Taxes
Reduction to income tax expenses		$ 146,000
Forecast
Income Taxes
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate	21.00%
Adjustments | Accounting Standards Update 2016-09 [Member]
Income Taxes
Reduction to income tax expenses		$ 146,000