Defined Benefit Plans - Net Periodic Cost (Benefit) (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Compensation and Retirement Disclosure [Abstract]
Expected return on plan assets, net of expenses	$ (2,890)	$ (2,983)	$ (8,669)	$ (8,949)
Interest cost on projected benefit obligation	1,732	2,052	5,230	6,157
Net amortization and deferral	1,585	1,748	4,691	5,246
SERP settlement costs	0	0	187	0
Net periodic expense (benefit)	$ 427	$ 817	$ 1,439	$ 2,454