Financial Instruments and Risk Management (Risk Management) (Details) (USD $)	Dec. 31, 2013	Dec. 31, 2012
Derivatives, Fair Value [Line Items]
Derivative, Net Gain Position	$ 22,902,000	$ 105,369,000
Derivative, Fair Value, Net [Abstract]
Gross Amounts Recognized	44,215,000	149,504,000
Derivative Liability, Fair Value, Gross Liability	(51,615,000)	(56,328,000)
Derivative, Fair Value, Net		93,176,000
Deferred Tax Assets (Liabilities), Net [Abstract]
Deferred tax assets (liabilities), net	(8,200,000)	(28,400,000)
Designated as Hedging Instrument
Derivative, Fair Value, Net [Abstract]
Gross Amounts Recognized		125,468,000
Derivative Liability, Fair Value, Net		(52,862,000)
Derivative, Fair Value, Net		72,606,000
Designated as Hedging Instrument | Accounts receivable
Derivative, Fair Value, Net [Abstract]
Gross Amounts Recognized		87,514,000
Derivative Liability, Fair Value, Gross Asset		(37,326,000)
Designated as Hedging Instrument | Other Assets
Derivative, Fair Value, Net [Abstract]
Gross Amounts Recognized		37,954,000
Derivative Liability, Fair Value, Gross Asset		(6,810,000)
Designated as Hedging Instrument | Other Liabilities
Derivative, Fair Value, Net [Abstract]
Derivative Liability, Fair Value, Gross Liability		(8,726,000)
Not Designated as Hedging Instrument
Derivative, Fair Value, Net [Abstract]
Gross Amounts Recognized	44,216,000	24,037,000
Derivative Liability, Fair Value, Gross Liability	(51,616,000)	(3,467,000)
Derivative, Fair Value, Net	(7,400,000)	20,570,000
Not Designated as Hedging Instrument | Accounts receivable
Derivative, Fair Value, Net [Abstract]
Gross Amounts Recognized	36,224,000	14,604,000
Derivative Liability, Fair Value, Gross Liability	(18,761,000)
Not Designated as Hedging Instrument | Long-term asset derivative instruments
Derivative, Fair Value, Net [Abstract]
Derivative Liability, Fair Value, Gross Liability	(2,553,000)
Not Designated as Hedging Instrument | Other Assets
Derivative, Fair Value, Net [Abstract]
Gross Amounts Recognized	7,992,000	9,433,000
Not Designated as Hedging Instrument | Accounts Payable
Derivative, Fair Value, Net [Abstract]
Derivative Liability, Fair Value, Gross Liability	(30,302,000)	(2,593,000)
Not Designated as Hedging Instrument | Other Liabilities
Derivative, Fair Value, Net [Abstract]
Derivative Liability, Fair Value, Gross Liability		(874,000)
Oil and Gas Operations
Derivative, Fair Value, Net [Abstract]
Derivative, Fair Value, Net		95,769,000
Oil and Gas Operations | Designated as Hedging Instrument
Derivative, Fair Value, Net [Abstract]
Gross Amounts Recognized		125,468,000
Derivative Liability, Fair Value, Net		(52,862,000)
Derivative, Fair Value, Net		72,606,000
Oil and Gas Operations | Designated as Hedging Instrument | Accounts receivable
Derivative, Fair Value, Net [Abstract]
Gross Amounts Recognized		87,514,000
Derivative Liability, Fair Value, Gross Asset		(37,326,000)	[1]
Oil and Gas Operations | Designated as Hedging Instrument | Other Assets
Derivative, Fair Value, Net [Abstract]
Gross Amounts Recognized		37,954,000
Derivative Liability, Fair Value, Gross Asset		(6,810,000)	[1]
Oil and Gas Operations | Designated as Hedging Instrument | Other Liabilities
Derivative, Fair Value, Net [Abstract]
Derivative Liability, Fair Value, Gross Liability		(8,726,000)
Oil and Gas Operations | Not Designated as Hedging Instrument
Derivative, Fair Value, Net [Abstract]
Gross Amounts Recognized	44,216,000	24,037,000
Derivative Liability, Fair Value, Gross Liability	(51,616,000)	(874,000)
Derivative, Fair Value, Net	(7,400,000)	23,163,000
Oil and Gas Operations | Not Designated as Hedging Instrument | Accounts receivable
Derivative, Fair Value, Net [Abstract]
Gross Amounts Recognized	36,224,000	14,604,000	[1]
Derivative Liability, Fair Value, Gross Liability	(18,761,000)
Oil and Gas Operations | Not Designated as Hedging Instrument | Long-term asset derivative instruments
Derivative, Fair Value, Net [Abstract]
Derivative Liability, Fair Value, Gross Liability	(2,553,000)
Oil and Gas Operations | Not Designated as Hedging Instrument | Other Assets
Derivative, Fair Value, Net [Abstract]
Gross Amounts Recognized	7,992,000	9,433,000	[1]
Oil and Gas Operations | Not Designated as Hedging Instrument | Accounts Payable
Derivative, Fair Value, Net [Abstract]
Derivative Liability, Fair Value, Gross Liability	(30,302,000)	0
Oil and Gas Operations | Not Designated as Hedging Instrument | Other Liabilities
Derivative, Fair Value, Net [Abstract]
Derivative Liability, Fair Value, Gross Liability		(874,000)
Natural Gas Distribution
Derivative, Fair Value, Net [Abstract]
Derivative, Fair Value, Net		(2,593,000)
Natural Gas Distribution | Designated as Hedging Instrument
Derivative, Fair Value, Net [Abstract]
Gross Amounts Recognized		0
Derivative Liability, Fair Value, Net		0
Derivative, Fair Value, Net		0
Natural Gas Distribution | Designated as Hedging Instrument | Accounts receivable
Derivative, Fair Value, Net [Abstract]
Gross Amounts Recognized		0
Derivative Liability, Fair Value, Gross Asset		0
Natural Gas Distribution | Designated as Hedging Instrument | Other Assets
Derivative, Fair Value, Net [Abstract]
Gross Amounts Recognized		0
Derivative Liability, Fair Value, Gross Asset		0
Natural Gas Distribution | Designated as Hedging Instrument | Other Liabilities
Derivative, Fair Value, Net [Abstract]
Derivative Liability, Fair Value, Gross Liability		0
Natural Gas Distribution | Not Designated as Hedging Instrument
Derivative, Fair Value, Net [Abstract]
Gross Amounts Recognized	0	0
Derivative Liability, Fair Value, Gross Liability	0	(2,593,000)
Derivative, Fair Value, Net	0	(2,593,000)
Natural Gas Distribution | Not Designated as Hedging Instrument | Accounts receivable
Derivative, Fair Value, Net [Abstract]
Gross Amounts Recognized	0	0
Derivative Liability, Fair Value, Gross Liability	0
Natural Gas Distribution | Not Designated as Hedging Instrument | Long-term asset derivative instruments
Derivative, Fair Value, Net [Abstract]
Derivative Liability, Fair Value, Gross Liability	0
Natural Gas Distribution | Not Designated as Hedging Instrument | Other Assets
Derivative, Fair Value, Net [Abstract]
Gross Amounts Recognized	0	0
Natural Gas Distribution | Not Designated as Hedging Instrument | Accounts Payable
Derivative, Fair Value, Net [Abstract]
Derivative Liability, Fair Value, Gross Liability	0	(2,593,000)
Natural Gas Distribution | Not Designated as Hedging Instrument | Other Liabilities
Derivative, Fair Value, Net [Abstract]
Derivative Liability, Fair Value, Gross Liability		0
Cash Flow Hedges | Macquarie Bank Limited
Derivatives, Fair Value [Line Items]
Derivative, Net Gain Position	8,600,000
Cash Flow Hedges | J Aron & Company
Derivatives, Fair Value [Line Items]
Derivative, Net Gain Position	$ 5,300,000

[1] Amounts classified in accordance with accounting guidance which permits offsetting fair value amounts recognized for multiple derivative instruments executed with the same counterparty under a master netting arrangement.