Income Taxes - Narrative (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Taxes
Income tax expense (benefit)	$ 0	$ 0	$ 0
Unrecognized tax benefit, which, if recognized, will not affect effective tax rate	2,239,000
Penalties and interest expense	0	$ 0	$ 0
Federal
Income Taxes
Net operating loss carryforwards	912,500,000
Operating loss carryforwards, subject to expiration	754,400,000
Operating loss carryforwards, not subject to expiration	158,100,000
Tax credits	6,900,000
State
Income Taxes
Net operating loss carryforwards	580,100,000
Tax credits	$ 1,900,000