Employee Benefit Plans - Components of Net Periodic Benefit Cost (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 4,798	$ 3,801	$ 14,735	$ 11,452
Interest cost	22,219	25,030	67,017	75,299
Expected return on plan assets	(33,414)	(32,098)	(100,427)	(96,260)
Amortization of prior service credit	(1,884)	(1,749)	(5,670)	(5,241)
Amortization of actuarial loss	20,535	17,314	62,744	52,809
Net periodic benefit cost	12,254	12,298	38,399	38,059
Other Post-Retirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Interest cost	32	66	107	200
Amortization of prior service credit	(239)	(232)	(717)	(698)
Amortization of actuarial loss	258	307	820	941
Net periodic benefit cost	$ 51	$ 141	$ 210	$ 443