Income Taxes - Provision for Income Taxes (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Current:
Federal	$ 0	$ 0	$ 0
State	1,250	436	476
Current income tax expense (benefit)	1,250	436	476
Deferred:
Federal	0	0	0
State	0	0	0
Deferred tax expense (benefit)	0	0	0
Income tax provision	$ 1,250	$ 436	$ 476