Components of Net Periodic Benefit Cost (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 15,834	$ 14,788	$ 13,857
Interest cost	26,791	27,363	28,519
Expected return on plan assets	(52,480)	(46,967)	(40,817)
Amortization of prior service cost (credit)	1,786	1,797	2,042
Amortization of actuarial losses	12,556	12,168	8,171
Net curtailment gain	0	(706)	(449)
Net periodic benefit cost (credit)	4,487	8,443	11,323
Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	682	830	862
Interest cost	1,605	2,051	2,441
Expected return on plan assets	0	0	0
Amortization of prior service cost (credit)	(2,684)	(2,616)	(2,582)
Amortization of actuarial losses	(234)	12	134
Net curtailment gain	0	0	0
Net periodic benefit cost (credit)	$ (631)	$ 277	$ 855