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, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 17	$ 16	$ 34	$ 32
Interest cost	1,477	1,596	2,954	3,192
Expected return on plan assets	(2,491)	(2,487)	(4,982)	(4,974)
Amortization:
Unrecognized net transition asset		(5)		(10)
Unrecognized prior service cost	2	2	4	4
Unrecognized loss	536	337	1,072	674
Net periodic pension credit	$ (459)	$ (541)	$ (918)	$ (1,082)