Schedule of Net Periodic Pension Costs (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Defined Benefit Pension Plans
Defined Benefit Plan Disclosure
Service cost	$ 2,787	$ 2,735	$ 3,655
Interest cost	15,670	17,466	17,716
Expected return on plan assets	(15,946)	(15,602)	(17,585)
Amortization of prior service cost	232	621	726
Net actuarial loss (gain)	23,237	12,583	(469)
Settlement loss (gain)		1,567	(3,113)
Total net periodic pension cost	25,980	19,370	930
Reversal of amortization items: Prior service cost	(232)	(621)	(726)
Total recognized in other comprehensive income	(232)	(621)	(726)
Total recognized in net periodic pension cost and other comprehensive income	25,748	18,749	204
Post-Retirement Benefit Plans
Defined Benefit Plan Disclosure
Service cost	67	59	57
Interest cost	437	539	668
Amortization of prior service cost	(599)	(598)	(416)
Net actuarial loss (gain)	83	981	(882)
Total net periodic pension cost	(12)	981	(573)
Net prior service credit arising during period			(3,279)
Reversal of amortization items: Prior service cost	599	598	416
Total recognized in other comprehensive income	599	598	(2,863)
Total recognized in net periodic pension cost and other comprehensive income	$ 587	$ 1,579	$ (3,436)