Defined Benefit Plans - Net Periodic Cost (Benefit) (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Compensation and Retirement Disclosure [Abstract]
Expected return on plan assets, net of expenses	$ (2,780)	$ (2,889)	$ (5,559)	$ (5,779)
Interest cost on projected benefit obligation	1,548	1,749	3,095	3,498
Net amortization and deferral	1,358	1,553	2,715	3,106
SERP settlement costs	0	187	0	187
Net periodic expense (benefit)	$ 126	$ 600	$ 251	$ 1,012