Components of Net Pension Costs (Detail) (Pension Plans, Defined Benefit, USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Pension Plans, Defined Benefit
Defined Benefit Plan Disclosure [Line Items]
Service cost for benefits earned during the year	$ 5,606	$ 4,952	$ 11,212	$ 9,904
Interest cost on accumulated benefit obligation	3,700	3,368	7,400	6,736
Expected return on assets	(3,027)	(3,386)	(6,054)	(6,772)
Net amortization of unrecognized amounts, Prior service cost	1,498	1,446	2,996	2,891
Net amortization of unrecognized amounts, Actuarial loss	1,229	103	2,458	206
Net Benefit Costs	$ 9,006	$ 6,483	$ 18,012	$ 12,965