Income Taxes - Effective Income Tax Rate Reconciliation (Details)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Effective income tax rate reconciliation
U.S. Federal statutory tax rate	(21.00%)	(21.00%)	(35.00%)
Deferred state taxes	1.20%	(1.90%)	(1.40%)
Common stock warrant liability		(1.00%)	4.20%
Provision to return and deferred tax asset adjustments			5.90%
Change in U.S. Federal statutory tax rate			33.50%
Other, net	(0.50%)	0.40%	2.00%
Change in valuation allowance	20.30%	12.90%	(9.20%)
Total effective income tax rate	0.00%	(10.60%)	0.00%