Net Periodic Benefit Cost (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Defined Benefit Plan Disclosure [Line Items]
Interest cost on projected benefit obligation	$ 1,534	$ 1,541	$ 1,490
Expected return on plan assets	(1,165)	(1,070)	(1,201)
Recognized net actuarial loss	1,194	1,159	1,156
Net periodic benefit cost	$ 1,563	$ 1,630	$ 1,445