Plan Assets and Benefit Obligations (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Change in benefit obligation:
Net benefit obligation at beginning of year	$ 52,841	$ 45,950
Interest cost	2,583	2,589	2,553
Actuarial loss	6,561	6,300	590
Gross benefits paid	(1,965)	(1,998)
Net benefit obligation at end of year	60,020	52,841	45,950
Change in plan assets:
Fair value of plan assets at beginning of year	32,643	32,797
Actual return on plan assets	3,562	(1,328)
Contributions	2,115	3,172
Gross benefits paid	(1,965)	(1,998)
Fair value of plan assets at end of year	36,355	32,643	32,797
Net benefit obligation in excess of plan assets	(23,665)	(20,198)
Balance sheet amounts:
Noncurrent liabilities	(23,665)	(20,198)
Total liabilities	(23,665)	(20,198)
Amounts recognized in accumulated other comprehensive income, net of tax consist of:
Net actuarial loss	21,342	18,466
Net amount recognized	$ 21,342	$ 18,466