Components of Net Pension Costs (Detail) (Pension Plans, Defined Benefit, 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
Defined Benefit Plan Disclosure [Line Items]
Service cost for benefits earned during the year	$ 5,606	$ 4,952	$ 16,818	$ 14,856
Interest cost on accumulated benefit obligation	3,700	3,368	11,100	10,105
Expected return on assets	(3,027)	(3,386)	(9,081)	(10,158)
Net amortization of unrecognized amounts, Prior service cost	1,498	1,446	4,495	4,337
Net amortization of unrecognized amounts, Actuarial loss	1,229	103	3,687	308
Net Benefit Costs	$ 9,006	$ 6,483	$ 27,019	$ 19,448