Income Taxes - Reconciliation of Effective Income Tax Rate (Details)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Effective Income Tax Rate Reconciliation
Tax at statutory federal rate (percent)	(21.00%)	(34.00%)
State tax, net of federal benefit (percent)	(5.30%)	(4.30%)
Measurement of deferred taxes as a result of tax reform (percent)	(0.00%)	68.70%
Tax credits (percent)	(0.70%)	(0.30%)
Change in deferred tax valuation allowance (percent)	26.20%	(32.60%)
Other (percent)	0.80%	2.50%
Total income tax expense (percent)	(0.00%)	(0.00%)