Income Taxes - Taxes Expense (Benefit) (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Current:
U.S.—Federal	$ (328)	$ 0	$ 0
U.S.—State	0	2	23
Deferred:
U.S.—Federal	426	(1,321)	(7,046)
U.S.—State	235	0	(889)
Total	$ 333	$ (1,319)	$ (7,912)