Income Taxes - Components of Income Tax Expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Current:
Federal	$ (29)	$ (29)	$ 0
State	0	0	0
Current tax expense (benefit)	(29)	(29)	0
Deferred:
Federal	29	29	(28)
State	0	0	0
Deferred tax expense (benefit)	29	29	(28)
Total income tax expense (benefit)	$ 0	$ 0	$ (28)