Benefit Plans - Change in Projected Benefit Obligation (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Change in projected benefit obligation:
Projected benefit obligation at beginning of year	$ 157,661	$ 176,339
Interest cost	6,681	6,889	$ 6,897
Actuarial loss (gain)	2,047	(17,177)
Benefits paid	(5,546)	(8,390)
Projected benefit obligation at end of year	161,306	157,661	176,339
Change in fair value of plan assets:
Fair value of plan assets at beginning of year	189,414	194,646
Actual return on plan assets	22,424	2,875
Employer contributions	347	283
Benefits paid	(5,546)	(8,390)
Fair value of plan assets at end of year	206,639	189,414	$ 194,646
Asset recognized	45,333	31,753
Accumulated benefit obligation	161,306	157,661
Accrued interest receivable	$ 606	$ 607