Components of Net Periodic Benefit Cost (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Defined benefit pension plans
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 3,789	$ 3,182	$ 7,688	$ 6,501
Interest cost	6,635	7,479	13,265	14,971
Expected return on plan assets	(7,329)	(7,764)	(14,658)	(15,524)
Amortization of prior service (credit) cost	(126)	11	(252)	21
Recognized actuarial loss	5,106	5,742	10,212	11,480
Total net periodic benefit cost	8,075	8,650	16,255	17,449
Postretirement benefit plans
Defined Benefit Plan Disclosure [Line Items]
Service cost	22	19	44	38
Interest cost	338	345	676	690
Recognized actuarial loss	40	30	80	60
Total net periodic benefit cost	$ 400	$ 394	$ 800	$ 788