Income Taxes - Reconciliation Effective Tax Rate (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Income Taxes
Provision for income taxes	$ 0	$ 0
Reconciliation of statutory federal income tax
Tax at statutory federal rate	(21.00%)	(34.00%)
State taxes, net of federal benefit	(1.70%)	(1.40%)
Stock-based compensation	1.50%	(0.80%)
Nondeductible executive compensation	0.90%
Change in valuation allowance	20.60%	(34.20%)
Federal tax rate change		70.20%
Other	(0.30%)	0.20%
Provision for income taxes	0.00%	0.00%