Senior Credit Facility (Details) (USD $)	1 Months Ended	9 Months Ended
Feb. 28, 2011	Sep. 30, 2011	Dec. 31, 2010
Senior Credit Facility (Textuals) [Abstract]
Borrowing base amount after it reset	$ 600,000,000
Initial borrowing base	325,000,000
Borrowings outstanding under line of credit facility		$ 0	$ 0
Applicable margin on senior credit facility		Interest rate margin varies from 1.0% to 1.75% in the case of borrowings based on the base rate and from 2.0% to 2.75% in the case of borrowings based on the Eurodollar rate.
Commitment fee on unused portion borrowing base		0.50%
Senior Credit Facility Covenants		maintain a current ratio (as defined) of at least 1 to 1 and a net leverage ratio that must be no greater than 4 to 1
Interest rate margin in case of base rate borrowing, lower range		1.00%
Interest rate margin in case of base rate borrowing, upper range		1.75%
Interest rate margin in case of Euro Dollar rate borrowing, lower range		2.00%
Interest rate margin in case of Euro Dollar rate borrowing, upper range		2.75%
Current ratio		1 to1
Net leverage ratio		4 to 1

Borrowing base amount after it reset.

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- Definition

Current ratio.

+ Details

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- Definition

Interest rate margin in case of base rate borrowing, lower range.

+ Details

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- Definition

Interest rate margin in case of base rate borrowing, upper range.

+ Details

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- Definition

Interest rate margin in case of Euro dollar rate borrowing, lower range.

+ Details

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- Definition

Interest rate margin in case of Euro dollar rate borrowing, upper range.

+ Details

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- Definition

Net leverage ratio.

+ Details

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- Definition

Senior Credit Facility.

+ Details

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- Definition

Unused borrowing capacity commitment fee.

+ Details

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- Definition

Description of minimum financial levels (for example, tangible net worth and working capital) and achievement of certain financial ratios (for example, working capital ratio and debt service coverage ratio), and adherence to certain clauses which generally require or restrict certain actions (for example, entering into a debt arrangement with equal or greater seniority, and selling or discontinuing a certain business segment or material subsidiary) to be in compliance with the covenant clauses of the debt agreement. May also include a discussion of the adverse consequences that would result if the entity violates or fails to satisfy the covenants.

+ References

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 22

-Article 5

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 129

-Paragraph 2, 4

+ Details

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- Definition

Description of the interest rate as being fixed or variable, and, if variable, identification of the index or rate on which the interest rate is based and the number of points or percentage added to that index or rate to set the rate, and other pertinent information, such as frequency of rate resets.

+ References

+ Details

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- Definition

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

+ References

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 19, 22

-Article 5

+ Details

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- Definition

Amount of current borrowing capacity under the credit facility considering any current restrictions on the amount that could be borrowed (for example, borrowings may be limited by the amount of current assets), but without considering any amounts currently outstanding under the facility.

+ References

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 19, 22

-Article 5

+ Details

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