Consolidated Financial Statements - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	6 Months Ended
Jun. 30, 2012	Dec. 31, 2012
Accounting Policies [Abstract]
Non-cash effect of accrued capital expenditures	$ 15.0
Capitalized interest	3.1
Increase (decrease) in retirement liabilities		(10.6)
Increase (decrease) in deferred income taxes (non-current)		(3.5)
Increase (decrease) in other current liabilities		7.2
Increase (decrease) in deferred income taxes (current)		$ 0.1

The amount of cash paid during the current period for interest that is capitalized.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 230

-SubTopic 10

-Section 50

-Paragraph 2

-URI http://asc.fasb.org/extlink&oid=6367179&loc=d3e4297-108586

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 95

-Paragraph 29

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.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 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 230

-SubTopic 10

-Section 45

-Paragraph 25

-Subparagraph (e)

-URI http://asc.fasb.org/extlink&oid=6943989&loc=d3e3536-108585

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration