Pension and Post-Retirement Plans (Detail) (USD $) In Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010
Pension Benefits
Components of net periodic (credit) expense:
Interest cost	$ 1,491	$ 1,515	$ 4,473	$ 4,543
Expected return on plan assets	(3,133)	(2,866)	(9,399)	(8,597)
Unrecognized past service liability		49		147
Amortization of unrecognized loss	1,190	1,286	3,569	3,858
Net periodic (credit) expense	(452)	(16)	(1,357)	(49)
Post-Retirement Benefits
Components of net periodic (credit) expense:
Interest cost	180	198	540	595
Service cost	1	1	4	3
Unrecognized past service liability	(62)	(62)	(187)	(187)
Amortization of unrecognized loss	103	78	308	235
Net periodic (credit) expense	$ 222	$ 215	$ 665	$ 646