Retirement Plans (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]
Service cost	$ 251	$ 236	$ 755	$ 708
Interest cost	446	447	1,341	1,341
Expected return on plan assets	(691)	(565)	(2,076)	(1,692)
Amortization of prior service cost	0	1	0	3
Amortization of net loss	298	112	892	333
Net periodic pension cost	$ 304	$ 231	$ 912	$ 693