Consolidated Statements of Operations and Comprehensive Income (Parenthetical) (USD $) In Thousands, unless otherwise specified	3 Months Ended	9 Months Ended
Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Prior service cost, tax	$ 28	$ 28	$ 84	$ 84
Actuarial loss, tax	$ 1,167	$ 720	$ 3,501	$ 2,160

Tax effect of the income statement impact of the reclassification adjustment for actuarial gain (loss) recognized as a component of net periodic benefit cost.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 220

-SubTopic 10

-Section 45

-Paragraph 15

-URI http://asc.fasb.org/extlink&oid=20435746&loc=d3e689-108580

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 220

-SubTopic 10

-Section 45

-Paragraph 12

-URI http://asc.fasb.org/extlink&oid=20435746&loc=d3e640-108580

Name:	us-gaap_OtherComprehensiveIncomeLossReclassificationPensionAndOtherPostretirementBenefitPlansNetGainLossRecognizedInNetPeriodicBenefitCostTax
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration