Income Taxes - Components of Income Tax Expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Current tax expense:
Federal	$ 0	$ 0
State	0	0
Foreign	0	0
Total current tax expense	0	0
Deferred tax expense:
Federal	3,555	(9,574)
State	822	2,061
Foreign	200	0
Total deferred tax expense	4,577	(7,513)
Change in deferred tax valuation allowance	(4,577)	7,513
Net deferred tax expense	0	0
Provision for income taxes	$ 0	$ 0