Schedule of 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
Pension Plans, Defined Benefit
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block
Service cost	$ 3,074	$ 2,815	$ 9,813	$ 8,446
Interest cost	5,561	5,808	17,754	17,425
Expected return on assets	(5,617)	(6,121)	(17,935)	(18,364)
Prior service cost (credit)	110	133	350	400
Actuarial loss (gain)	2,920	1,581	9,323	4,743
Settlement charge	255	332	779	346
Net periodic benefit cost (credit)	6,303	4,548	20,084	12,996
Other Postretirement Benefit Plans, Defined Benefit
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block
Service cost	57	88	171	263
Interest cost	309	556	926	1,669
Prior service cost (credit)	(814)	(435)	(2,442)	(1,306)
Actuarial loss (gain)	(71)	(21)	(212)	(64)
Net periodic benefit cost (credit)	$ (519)	$ 188	$ (1,557)	$ 562