Oil and Gas Properties (Narratives) (Details) $ in Millions	12 Months Ended
Dec. 31, 2015 USD ($) $ / Mcf	Dec. 31, 2014 USD ($) $ / Mcf	Dec. 31, 2013 USD ($) $ / Mcf
Oil And Gas Property [Abstract]
DD&A per Mcfe \| $ / Mcf	1.38	1.18	1.05
Ceiling test limitation	$ 3,100.0	$ 0.0	$ 0.0
Total interest on outstanding debt	185.0	146.6
Capitalized interest detail	$ 13.1	$ 20.4

Amortization computed on the basis of physical units, with oil and gas converted to a common unit of measure on the basis of their approximate relative energy content.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 932
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-10.(c)(7)(i))
-URI http://asc.fasb.org/extlink&oid=27015464&loc=d3e511914-122862

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 10
-Paragraph c
-Subparagraph 7
-Article 4

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Amount of interest capitalized during the period.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Glossary Allowance for Funds Used during Construction
-URI http://asc.fasb.org/extlink&oid=6504829

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=6450988&loc=d3e26243-108391

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Aggregate amount of interest expense on all borrowings.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 225
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-04.7,8)
-URI http://asc.fasb.org/extlink&oid=6879574&loc=d3e536633-122882

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No definition available.

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The excess of unamortized costs capitalized within a cost center, less related deferred income taxes, over the cost center ceiling limitation, which is charged to expense for oil and gas producing companies that use full cost method of accounting for investments in oil and gas producing properties.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 932
-SubTopic 360
-Section S99
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=27015634&loc=d3e516453-122869

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 10
-Paragraph c
-Subparagraph 4(ii)
-Article 4

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