Acquisitions & Divestitures (Tables)

6 Months Ended

Jun. 30, 2015

Business Acquisition, Pro Forma Information, Nonrecurring Adjustment [Line Items]

Business Combination, Separately Recognized Transactions [Table Text Block]

Consideration:
Total consideration	$	941.8
Amounts recognized for fair value of assets acquired and liabilities assumed:
Proved properties	$	472.1
Unproved properties	480.6
Asset retirement obligations	(9.7		)
Liabilities assumed	(1.2		)
Total fair value	$	941.8

Business Acquisition, Pro Forma Information [Table Text Block]

		Six Months Ended
		June 30, 2014
		Actual			Pro forma
	(in millions, except per share data)
Revenues		$	1,704.7		$	1,730.8
Net income		$	(52.6	)	$	(45.6	)
Earnings per common share
Basic		$	(0.29	)	$	(0.25	)
Diluted		$	(0.29	)	$	(0.25	)