Fair Values of Pension Plan Assets (Parenthetical) (Detail)	Dec. 31, 2011
Mutual Funds \| Equity
Schedule of Pension and Other Postretirment Benefits Changes in Benefit Obligation and Fair Value of Plan Assets [Line Items]
Percentage of investments	50.00%
Mutual Funds \| Fixed Income Investments
Schedule of Pension and Other Postretirment Benefits Changes in Benefit Obligation and Fair Value of Plan Assets [Line Items]
Percentage of investments	50.00%
Common Collective Trusts \| Equity
Schedule of Pension and Other Postretirment Benefits Changes in Benefit Obligation and Fair Value of Plan Assets [Line Items]
Percentage of investments	65.00%
Common Collective Trusts \| Fixed Income Investments
Schedule of Pension and Other Postretirment Benefits Changes in Benefit Obligation and Fair Value of Plan Assets [Line Items]
Percentage of investments	35.00%

The aggregate percentage of the fair value of investments (categorized by debt securities, equity securities, real estate and other plan assets) to the fair value of total plan assets held as of the measurement date.

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 132R

-Paragraph 5

-Subparagraph d(1)

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 715

-SubTopic 20

-Section 50

-Paragraph 5

-Subparagraph (c)

-URI http://asc.fasb.org/extlink&oid=6962843&loc=d3e2446-114920

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 715

-SubTopic 20

-Section 50

-Paragraph 1

-Subparagraph (d)(1)

-URI http://asc.fasb.org/extlink&oid=6962843&loc=d3e1928-114920

Name:	us-gaap_DefinedBenefitPlanWeightedAverageAssetAllocations
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant