Components of net periodic pension cost (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Pension Plans, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan Interest Cost	$ 7,495	$ 7,784	$ 22,486	$ 23,354
Expected return on plan assets	(9,810)	(10,840)	(29,430)	(32,521)
Defined Benefit Plan Amortization Of Net Gains Losses	5,426	2,829	16,277	8,486
Defined Benefit Plan Net Periodic Benefit Cost	3,111	(227)	9,333	(681)
Other Pension Plans Defined Benefit Member
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan Interest Cost	393	395	1,179	1,186
Expected return on plan assets	(526)	(450)	(1,578)	(1,350)
Defined Benefit Plan Amortization Of Net Gains Losses	323	148	969	443
Defined Benefit Plan Net Periodic Benefit Cost	$ 190	$ 93	$ 570	$ 279