Income Taxes - Component of Income Taxes Expenses (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Components of income tax expense (benefit):
Currently payable (receivable)	$ 1,500	$ 100	$ 800
Deferred income tax expense (benefit)	(4,300)	(28,700)	4,200
Income tax expense (benefit)	$ (2,777)	$ (28,611)	$ 5,003