Acquisitions & Divestitures (Narrative) (Details) (USD $) In Millions, unless otherwise specified	4 Months Ended	9 Months Ended			3 Months Ended	9 Months Ended
	Jun. 30, 2014	Sep. 30, 2014 acre		Sep. 30, 2014 Term Loan due 2017 [Member]	Sep. 30, 2014 Permian Basin [Member]	Sep. 30, 2014 Permian Basin [Member]
Business Acquisition [Line Items]
Liabilities incurred		$ 15.5	[1]			$ 9.7
Aggregate sale price of assets disposed		702.3
Pretax loss on sale of assets		210.4
Consideration Held In Escrow Pending Title Defects		28.7
Payments to Acquire Businesses, Gross					941.8
Payments to Acquire Businesses Net		941.8
Net acres of producing and undeveloped oil and gas properties		26,500
Number of vertical producing wells		270
Escrow Deposit		50.0
Borrowings to Fund Acquisition				300.0
Business Combination, Pro Forma Information, Revenue of Acquiree since Acquisition Date, Actual	114.2
Business Combination, Pro Forma Information, Earnings or Loss of Acquiree since Acquisition Date, Actual	23.1
Business Acquisition, Transaction Costs		0.6
Debt Issuance Cost		$ 1.1

[1] Additions include $9.7 million related to the Permian Basin Acquisition (see Note 3 - Acquisitions and Divestitures).