Fair Value Measurements (Details 1) (USD $) In Thousands, unless otherwise specified	3 Months Ended
Jun. 30, 2013	Mar. 31, 2013	Jun. 30, 2012	Mar. 31, 2012
Interest rate derivatives and swaptions
Beginning and ending balances for the Company's fair value measurements using Level 3 inputs
Liability, Beginning Balance	$ 0	$ 0	$ 0	$ (2,178)
Unrealized gains (losses) included in other comprehensive income	0	0	0	0
Transfers to level 2		0		2,178
Liability, Ending Balance	0	0	0	0
Convertible preferred securities
Beginning and ending balances for the Company's fair value measurements using Level 3 inputs
Asset, Beginning Balance	17,710	17,220	20,360	20,360
Unrealized gains (losses) included in other comprehensive income	0	490	(3,010)	0
Transfers to level 2		0		0
Asset, Ending Balance	17,710	17,710	17,350	20,360
Commodity derivatives, net
Beginning and ending balances for the Company's fair value measurements using Level 3 inputs
Asset, Beginning Balance	0	0	0	2,467
Unrealized gains (losses) included in other comprehensive income	0	0	0	0
Transfers to level 2		0		(2,467)
Asset, Ending Balance	$ 0	$ 0	$ 0	$ 0

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Transfers out of assets measured at fair value and categorized within Level 3 of the fair value hierarchy that have taken place during the period.

+ References

+ Details

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- Definition

This element represents an asset measured at fair value using significant unobservable inputs (Level 3) which is required for reconciliation purposes of beginning and ending balances.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 820

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (c)

-URI http://asc.fasb.org/extlink&oid=7578670&loc=d3e19207-110258

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 157

-Paragraph 32

-Subparagraph c

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.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

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
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- Definition

Amount of gain (loss) recognized in other comprehensive income, arising from liabilities measured at fair value on a recurring basis using unobservable inputs (level 3).

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 820

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (c)(1a)

-URI http://asc.fasb.org/extlink&oid=7578670&loc=d3e19207-110258

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 157

-Paragraph 32

-Subparagraph c(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.

+ Details

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- Definition

This element represents a liability measured at fair value using significant unobservable inputs (Level 3) which is required for reconciliation purposes of beginning and ending balances.

+ References

+ Details

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