Schedule of Components of Net Periodic Cost (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Summary of Components of Net Periodic Benefit Cost and Other Changes in Plan Assets and Benefit Obligations Recognized in Other Comprehensive Income [Line Items]
Service cost	$ 1,144	$ 1,162	$ 1,140
Interest cost	4,659	5,047	4,958
Expected return on plan assets	(7,301)	(6,566)	(5,151)
Recognized actuarial loss	4,219	2,427	2,538
Net periodic cost	$ 2,721	$ 2,070	$ 3,485