Net Periodic Benefit Cost (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Defined Benefit Plan Disclosure [Line Items]
Interest cost on projected benefit obligation	$ 374	$ 383	$ 1,151	$ 1,151
Expected return on plan assets	(220)	(267)	(874)	(801)
Recognized net actuarial loss	197	297	896	890
Net periodic benefit cost	$ 351	$ 413	$ 1,173	$ 1,240