Employee Retirement Plans - Qualified Defined-Benefit Pension Plan Weighted Average Asset Allocation (Detail) (Qualified Plans [Member])	Dec. 31, 2012	Dec. 31, 2011
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Weighted average asset allocation	100.00%	100.00%
Equities Securities [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Weighted average asset allocation	44.00%	44.00%
Debt Securities [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Weighted average asset allocation	41.00%	39.00%
Other [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Weighted average asset allocation	15.00%	17.00%

Percentage of fair value of investments (categorized by debt securities, equity securities, real estate and other plan assets) to the fair value of plan assets held.

Reference 1: 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=21915506&loc=d3e2446-114920

Reference 2: 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=21915506&loc=d3e1928-114920

Reference 3: 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-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.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.

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Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant