Components of net unrecognized benefits costs (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Schedule Of Net Unrecognized Benefits Costs Of Accumulated Other Comprehensive Income [Line Items]
Included in accumulated other comprehensive income (loss) Balance	$ 11,239	$ 10,618	$ 10,806
Additions during the year	(649)	443	968
Reclassifications due to recognition as net periodic pension cost	(1,194)	(1,159)	(1,156)
Increase related to change in discount rate assumption	5,483	1,337
Included in accumulated other comprehensive income (loss) Balance	14,879	11,239	10,618
Applicable tax effect	(5,933)
Included in accumulated other comprehensive income (loss) net of tax effect at December 31, 2012	8,946
Amount expected to be recognized as part of net periodic pension cost in the next fiscal year	$ 1,350