Pension and Post-Retirement Plans (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Pension Benefits
Components of net periodic (credit) expense:
Interest cost	$ 1,470	$ 1,516	$ 4,411	$ 4,547
Expected return on plan assets	(3,906)	(4,390)	(11,720)	(13,169)
Amortization of net actuarial loss	2,262	2,052	6,786	6,156
Net periodic (credit) expense	(174)	(822)	(523)	(2,466)
Post-Retirement Benefits
Components of net periodic (credit) expense:
Interest cost	160	175	479	525
Service cost	1	1	3	3
Amortization of prior-service costs	(62)	(62)	(187)	(187)
Amortization of net actuarial loss	81	96	245	287
Net periodic (credit) expense	$ 180	$ 210	$ 540	$ 628