Retirement Plans - Net Periodic Benefit Credit for Defined Benefit Plans (Detail) - Defined Benefit Plans [Member] - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ (4)	$ 18	$ (12)	$ 52
Interest cost	1,521	1,470	4,609	4,424
Expected return on plan assets	(2,354)	(2,491)	(7,060)	(7,473)
Amortization:
Unrecognized prior service cost	2	2	6	6
Unrecognized loss	584	518	1,800	1,590
Net periodic pension credit	$ (251)	$ (483)	$ (657)	$ (1,401)