Derivative Instruments and Hedging Activities - Narrative (Details) - USD ($)	12 Months Ended
	Dec. 31, 2014	Apr. 01, 2014
Derivative [Line Items]
Unrealized losses included in accumulated other comprehensive income, reclassified into natural gas and crude oil revenues , pre-tax		$ 73,400,000
Unrealized losses included in accumulated other comprehensive income, reclassified into natural gas and crude oil revenues , net of tax	$ 0	$ 44,200,000
Gain (loss) on cash flow hedge ineffectiveness	$ 0