Employee Benefit Plans - 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
Defined Benefit Plan Disclosure [Line Items]
Curtailment gain	$ (23,507)
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	15,254	13,039	12,312
Interest cost	100,338	97,293	95,453
Expected return on plan assets	(128,208)	(124,150)	(114,166)
Amortization of prior service credit	(7,270)	(6,970)	(6,979)
Amortization of actuarial loss	70,161	53,039	35,264
Curtailment gain	(23,507)
Net periodic benefit cost	26,768	32,251	21,884
Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost
Interest cost	267	474	605
Expected return on plan assets
Amortization of prior service credit	(930)	(930)	(1,059)
Amortization of actuarial loss	1,254	1,708	1,759
Curtailment gain
Net periodic benefit cost	$ 591	$ 1,252	$ 1,305