Components of Net Periodic Benefit Cost (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Changes in Plan Assets and Benefit Obligations Recognized in Other Comprehensive Income
Reclassification of actuarial loss to net periodic pension benefit cost	$ (11,965)	$ (7,710)	$ (3,590)
Reclassification of prior service cost to net periodic pension benefit cost	(11,965)	(7,710)	(3,590)
Weighted-average assumptions used to determine net periodic benefit cost for years ended December 31
Expected return on plan assets	7.50%	8.00%
Rate of compensation increase (for salary-related plans)	3.50%
Pension Plans, Defined Benefit
Components of Net Periodic Pension Benefit Cost
Service cost	22,349	20,762	19,217
Interest cost	43,194	42,383	41,621
Expected return on plan assets	(48,780)	(49,480)	(50,122)
Amortization of prior service cost	274	340	460
Amortization of actuarial loss	19,526	11,670	5,752
Net periodic pension benefit cost	36,563	25,675	16,928
Changes in Plan Assets and Benefit Obligations Recognized in Other Comprehensive Income
Net actuarial loss (gain)	63,981	90,886	(17,413)
Prior service cost	1,286	0	0
Reclassification of actuarial loss to net periodic pension benefit cost	(19,526)	(11,670)	(5,752)
Reclassification of prior service cost to net periodic pension benefit cost	(274)	(340)	(460)
Amount recognized in other comprehensive income	45,467	78,876	(23,625)
Amount recognized in net periodic pension benefit cost and other comprehensive income	$ 82,030	$ 104,551	$ (6,697)
Weighted-average assumptions used to determine net periodic benefit cost for years ended December 31
Discount rate	4.96%	5.49%	5.92%
Expected return on plan assets	8.00%	8.00%	8.25%
Rate of compensation increase (for salary-related plans)	3.50%	3.50%	3.40%
Weighted-average assumptions used to determine benefit obligation at December 31
Discount rate	4.19%	4.96%	5.49%
Rate of compensation increase (for salary-related plans)	3.50%	3.50%	3.50%