Income Taxes - Components (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Current:
U.S. federal	$ 0	$ 0	$ 1
State	11	10	26
Total current	11	10	27
Deferred:
U.S. Federal	0	(125)	0
State	0	0	0
Total deferred	0	(125)	0
Provision for income taxes	$ 11	$ (115)	$ 27