Retirement Plans and Other Postretirement Benefits - Components of Net Periodic Benefit Cost (Income) (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Retirement Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 661	$ 756	$ 528
Interest cost	2,071	1,953	1,900
Expected return on plan assets	(3,041)	(3,100)	(2,929)
Amortization of net actuarial loss	1,296	1,308	649
Accretion of prior service cost	(283)	(280)	(281)
Settlement cost	1,434	0	0
Net periodic benefit (income) cost	2,138	637	(133)
Other Post Retirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	46	59	75
Interest cost	133	110	128
Expected return on plan assets	0	0	0
Amortization of net actuarial loss	25	54	17
Accretion of prior service cost	0	0	(7)
Settlement cost	0	0	0
Net periodic benefit (income) cost	$ 204	$ 223	$ 213