Income Taxes - Narrative (Details) - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Taxes
Income tax expense (benefit)	$ 0	$ 0	$ 0
Increase in valuation allowance	26,900,000
Unrecognized tax benefits	2,563,000	2,239,000
Penalties and interest expense	0	$ 0	$ 0
Federal
Income Taxes
Net operating loss carryforwards	974,300,000
Operating loss carryforwards, subject to expiration	754,200,000
Operating loss carryforwards, not subject to expiration	220,100,000
Tax credits	8,000,000.0
State
Income Taxes
Net operating loss carryforwards	681,800,000
Tax credits	$ 2,100,000