Defined Benefit Plans - Net Periodic Cost (Benefit) (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Compensation and Retirement Disclosure [Abstract]
Expected return on plan assets, net of expenses	$ (2,889)	$ (2,983)	$ (5,779)	$ (5,966)
Interest cost on projected benefit obligation	1,749	2,053	3,498	4,105
Net amortization and deferral	1,553	1,749	3,106	3,498
SERP settlement costs	187	0	187	0
Net periodic expense (benefit)	$ 600	$ 819	$ 1,012	$ 1,637