Summary of Significant Accounting Policies - Income Taxes (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Operating loss carryforwards
Valuation allowance for deferred tax assets	$ 7,005,000	$ 8,291,000
State net operating loss carryforward
Operating loss carryforwards
Valuation allowance for deferred tax assets	7,005,000
Decrease in valuation allowances	$ 1,286,000	$ 163,000	$ 1,872,000