Income Taxes - Summary of Income Tax Expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Current:
Federal	$ 0	$ 0
State	0	0
Current income tax expense (benefit)	0	0
Deferred:
Federal	(212)	(73)
State	(18)	(6)
Deferred income tax expense (benefit)	(230)	(79)
Income tax (benefit) expense	$ (230)	$ (79)