Schedule of Debt Outstanding (Parenthetical) (Detail) (USD $) In Millions, unless otherwise specified	1 Months Ended	6 Months Ended
Jun. 30, 2012	Jun. 30, 2012	Dec. 31, 2011
Debt Instrument [Line Items]
Revolving Credit Facility maturity date	Dec. 31, 2016
Revolving Credit Facility
Debt Instrument [Line Items]
Revolving Credit Facility maturity date	Dec. 31, 2016
Weighted average rate	1.70%	1.70%	1.00%
Senior Notes interest payable dates		interest payable periodically at variable interest rates
Senior Notes 6.25% Due 2013
Debt Instrument [Line Items]
Interest rate stated percentage of Senior Notes	6.25%	6.25%
Note maturity date		Mar. 15, 2013
Senior Notes interest payable dates		interest payable semi-annually in March and September at 6.25%.
Senior Notes 6.75% Due 2014
Debt Instrument [Line Items]
Interest rate stated percentage of Senior Notes	6.75%	6.75%
Note maturity date		Jan. 31, 2014
Senior Notes interest payable dates		interest payable semi-annually in January and July at 6.75%.
Redeemable aggregate principal amount	60.0	60.0
Senior Notes 7.75% Due 2017
Debt Instrument [Line Items]
Interest rate stated percentage of Senior Notes	7.75%	7.75%
Note maturity date		Jun. 01, 2017
Senior Notes interest payable dates		interest payable semi-annually in June and December at 7.75%.
Notes issued with a discount	13.4	13.4
Notes, unamortized	9.2	9.2	10.0

The amount of debt discount that was originally recognized at the issuance of the instrument that has yet to be amortized.

+ References+ Details

The amount of debt discount (net of debt premium) that was originally recognized at the issuance of the instrument that has yet to be amortized.

+ References

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

-Publisher AICPA

-Name Accounting Principles Board Opinion (APB)

-Number 21

-Paragraph 16

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.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 835

-SubTopic 30

-Section 45

-Paragraph 3

-URI http://asc.fasb.org/extlink&oid=6451184&loc=d3e28555-108399

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 835

-SubTopic 30

-Section 45

-Paragraph 4

-URI http://asc.fasb.org/extlink&oid=6451184&loc=d3e28567-108399

Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 835

-SubTopic 30

-Section 55

-Paragraph 8

-URI http://asc.fasb.org/extlink&oid=6584090&loc=d3e28878-108400

Reference 5: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 835

-SubTopic 30

-Section 45

-Paragraph 2

-URI http://asc.fasb.org/extlink&oid=6451184&loc=d3e28551-108399

Reference 6: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 835

-SubTopic 30

-Section 45

-Paragraph 1A

-URI http://asc.fasb.org/extlink&oid=6451184&loc=d3e28541-108399

Reference 7: http://www.xbrl.org/2003/role/presentationRef

-Publisher AICPA

-Name Accounting Principles Board Opinion (APB)

-Number 21

-Paragraph 20

-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.

+ Details