Summary of Long-Term Debt (Detail) (USD $)	Sep. 30, 2013	Dec. 31, 2012
Debt Instrument [Line Items]
Revolving credit facility	$ 128,000,000	$ 0
Total	1,203,000,000	594,759,000
10.375% Senior Unsecured Notes due 2016
Debt Instrument [Line Items]
Senior notes	0	294,759,000
Principal amount	0	300,000,000
7.25% Senior Unsecured Notes due 2019
Debt Instrument [Line Items]
Senior notes	300,000,000	300,000,000
8.5% Senior Notes due 2020
Debt Instrument [Line Items]
Senior notes	$ 775,000,000	$ 0

The stated principal amount of the debt instrument at time of issuance, which may vary from the carrying amount because of unamortized premium or discount.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 835

-SubTopic 30

-Section 45

-Paragraph 2

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-Publisher AICPA

-Name Accounting Principles Board Opinion (APB)

-Number 21

-Paragraph 16, 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-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.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.

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- Definition

Amount borrowed under the credit facility as of the balance sheet date.

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Carrying amount of long-term debt, net of unamortized discount or premium, including current and noncurrent amounts. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

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Carrying value as of the balance sheet date of Notes with the highest claim on the assets of the issuer in case of bankruptcy or liquidation (with maturities initially due after one year or beyond the operating cycle if longer), excluding current portion. Senior note holders are paid off in full before any payments are made to junior note holders.

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