Income Taxes (Details) - USD ($)	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Statutory federal income tax rate
Statutory federal income tax rate (as a percent)	21.00%	21.00%	21.00%
Deferred tax assets:
Valuation allowance against deferred tax assets	$ 137,700,000	$ 131,309,000
Tax Credit Carryforwards
Unrecognized tax benefits	619,000	$ 619,000	$ 1,116,000
Unrecognized Tax Benefits Penalties and Interest
Interest expense or penalties related to unrecognized tax benefits	0
Research and development
Tax Credit Carryforwards
Unrecognized tax benefits	600,000
Federal
Deferred tax assets:
Net operating loss carryforwards	483,100,000
Federal | Tax Year 2027
Deferred tax assets:
Net operating loss carryforwards	$ 9,800,000
Net operating loss carryforwards, expiration year	2027
Federal | Minimum
Income Tax Uncertainties [Abstract]
Tax years	2018
Federal | Maximum
Income Tax Uncertainties [Abstract]
Tax years	2020
Federal | Research and development
Tax Credit Carryforwards
Tax credit carryforwards	$ 30,000
Tax credit carryforwards, expiration year	2029
State
Deferred tax assets:
Net operating loss carryforwards	$ 330,100,000
State | Tax Year 2017
Deferred tax assets:
Net operating loss carryforwards	$ 8,300,000
Net operating loss carryforwards, expiration year	2017
State | Minimum
Income Tax Uncertainties [Abstract]
Tax years	2017
State | Maximum
Income Tax Uncertainties [Abstract]
Tax years	2020
State | Research and development
Tax Credit Carryforwards
Tax credit carryforwards	$ 2,700,000