Income Taxes - Expense for Income Taxes (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Current Federal	$ 0	$ 1,402	$ 0
Current State	0	0	0
Deferred Federal	(1,777)	0	0
Deferred State	(50)	0	0
Income tax (expense) benefit	$ (1,827)	$ 1,402	$ 0