Components of Change in Benefit Obligation of Pension Plans (Detail) (Pension Plans, Defined Benefit, USD $)	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010
Pension Plans, Defined Benefit
Employee Benefits Disclosure [Line Items]
Benefit obligation, at beginning of year	$ 427,213,000	$ 386,316,000
Interest cost	22,663,000	22,685,000
Benefits paid	(15,493,000)	(15,516,000)
Actuarial loss	48,226,000	33,728,000
Benefit obligation, at end of year	$ 482,609,000	$ 427,213,000