Components of Net Periodic Pension Cost (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 286	$ 247	$ 572	$ 581
Interest cost	1,165	1,071	2,330	2,523
Expected return on assets	(2,111)	(1,774)	(3,651)	(3,283)
Recognized actuarial loss	1,055	470	2,110	1,214
Net periodic pension cost	$ 395	$ 14	$ 1,361	$ 1,035