Retirement Plans - Net Periodic Benefit Credit for Defined Benefit Plans (Detail) - Defined Benefit Plans [Member] - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ (4)	$ 17	$ (8)	$ 34
Interest cost	1,544	1,477	3,088	2,954
Expected return on plan assets	(2,353)	(2,491)	(4,706)	(4,982)
Amortization:
Unrecognized prior service cost	2	2	4	4
Unrecognized loss	608	536	1,216	1,072
Net periodic pension credit	$ (203)	$ (459)	$ (406)	$ (918)