Pension and Post-Retirement Plans (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Pension Benefits
Components of net periodic (credit) expense:
Interest cost	$ 1,516	$ 1,474	$ 4,547	$ 4,422
Expected return on plan assets	(4,390)	(4,859)	(13,169)	(14,577)
Amortization of net actuarial loss	2,052	822	6,156	2,466
Net periodic (credit) expense	(822)	(2,563)	(2,466)	(7,689)
Post-Retirement Benefits
Components of net periodic (credit) expense:
Interest cost	175	190	525	569
Service cost	1	1	3	3
Amortization of past service liability	(62)	(62)	(187)	(186)
Amortization of net actuarial loss	96	118	287	354
Net periodic (credit) expense	$ 210	$ 247	$ 628	$ 740