Components of Net Periodic Benefit Cost (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Interest cost	$ 2,583	$ 2,589	$ 2,553
Expected return on assets	(2,559)	(2,644)	(2,329)
Amortization of actuarial net loss	918	582	590
Net periodic benefit cost	$ 942	$ 527	$ 814