Components of net periodic pension cost (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011
Pension Plans, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan Interest Cost	$ 7,495	$ 7,785
Expected return on plan assets	(9,810)	(10,840)
Defined Benefit Plan Amortization Of Net Gains Losses	5,426	2,828
Defined Benefit Plan Net Periodic Benefit Cost	3,111	(227)
Other Pension Plans Defined Benefit Member
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan Interest Cost	393	395
Expected return on plan assets	(526)	(451)
Defined Benefit Plan Amortization Of Net Gains Losses	323	148
Defined Benefit Plan Net Periodic Benefit Cost	$ 190	$ 92