Company's Pension and Post-Retirement Plans (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Pension Benefits
Components of net periodic expense (credit):
Interest cost	$ 1,364	$ 1,471	$ 2,728	$ 2,943
Expected return on plan assets	(4,147)	(3,314)	(8,294)	(6,628)
Amortization of net actuarial loss	2,351	2,434	4,702	4,868
Net periodic (credit) expense	(432)	591	(864)	1,183
Post-Retirement Benefits
Components of net periodic expense (credit):
Interest cost	171	160	342	320
Service cost	1	2	2	3
Amortization of prior-service loss	(62)	(62)	(124)	(124)
Amortization of net actuarial loss	164	126	328	253
Net periodic (credit) expense	$ 274	$ 226	$ 548	$ 452