Components of Net Periodic Benefit 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
Defined benefit pension plans
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 3,326	$ 2,961	$ 9,827	$ 9,166
Interest cost	7,501	7,124	22,472	21,777
Expected return on plan assets	(7,837)	(6,807)	(23,361)	(19,409)
Amortization of prior service cost	(398)	427	(377)	1,384
Recognized actuarial loss (gain)	5,923	4,233	17,403	11,501
Settlement loss	3,534		3,534
Total net periodic benefit cost	12,049	7,938	29,498	24,419
Postretirement benefit plans
Defined Benefit Plan Disclosure [Line Items]
Service cost	21	15	59	55
Interest cost	369	307	1,059	1,182
Recognized actuarial loss (gain)	27	(107)	87	(36)
Total net periodic benefit cost	$ 417	$ 215	$ 1,205	$ 1,201