Acquisitions & Divestitures (Tables)

3 Months Ended

Mar. 31, 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]

		Three Months Ended
		March 31,
		2014		2014
		Actual		Pro forma
	(in millions, except per share data)
Revenues		$	817.5	$	843.6
Net income		$	39.7	$	46.7
Earnings per common share
Basic		$	0.22	$	0.26
Diluted		$	0.22	$	0.26