Income Taxes - Component of Income Taxes Expenses (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Components of income tax benefit:
Currently payable (receivable)	$ (200)	$ (100)	$ 1,500
Deferred income tax benefit	(15,200)	(5,500)	(4,300)
Income tax benefit	$ (15,361)	$ (5,634)	$ (2,777)