Retirement Plans - Schedule of Accumulated Benefit Obligation, Change in Benefit Obligation, Change in Plan Assets, Plans' Funded Status and Amount Included in Consolidated Balance Sheet (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Compensation and Retirement Disclosure [Abstract]
Accumulated benefit obligation	$ 150,754	$ 156,589
Projected benefit obligation at beginning of year	156,924	139,731
Service cost	(14)	62
Interest cost	5,897	6,411
Actuarial (gain) loss	(3,381)	21,253
Benefits paid	(8,411)	(10,533)
Projected benefit obligation at end of year	151,015	156,924
Fair value of plan assets at beginning of year	140,140	139,737
Actual return on plan assets	(331)	9,613
Corporation contribution	1,364	1,323
Benefits paid	(8,411)	(10,533)
Fair value of plan assets at end of year	132,762	140,140
Funded status of plans	$ (18,253)	$ (16,784)