Income Taxes - Schedule of Provision for Federal Income Taxes (Detail) - USD ($) $ in Thousands	3 Months Ended			12 Months Ended
	Dec. 31, 2017	Jun. 30, 2017	Dec. 31, 2016	Dec. 31, 2017	Dec. 31, 2016
Current
Federal				$ (247)	$ 247
Total current tax expense				(247)	247
Deferred
Total income tax expense	$ (375)	$ 128	$ 247	$ (247)	$ 247