Derivative Instruments (Narrative) (Details) (USD $)	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Dec. 31, 2012
Derivative [Line Items]
Fair Value Asset/(Liability)	$ 11,300		$ 11,300		$ 16,200
Gain Recognized On Settled Commodity Contracts	13,400	13,000	36,700	90,100
Gain (Loss) on Fair Value Hedge Ineffectiveness, Net	0	0	0	0
Affiliate Balances, Offsetting Derivative Assets, Gross Amounts of Recognized Assets	30,800		30,800		90,600
Affiliate Balances, Offsetting Derivative Liabilities, Gross Amounts Of Recognized Liabilities	19,700		19,700		24,100
Accumulated other comprehensive loss	(10,100)		(10,100)		(17,000)
Unrealized gains (losses) due to natural gas and oil property impairments
Derivative [Line Items]
Accumulated other comprehensive loss	(10,100)		(10,100)
Cash Flow Hedge (Loss) to be Reclassified within Twelve Months			(5,100)
Net Deferred Losses To Be Reclassified Into Net Income In Later Periods			(5,000)
Allocation To Limited Partner Only | Other Comprehensive Income (Loss)
Derivative [Line Items]
Net Derivative Gains Limited Partner			17,500
Allocation To MGP Only | Other Comprehensive Income (Loss)
Derivative [Line Items]
Reclassification Adjustment For Gain Recognized On Property Impairments			32,500
Accounts receivable monetized gains-affiliate
Derivative [Line Items]
Affiliate Balances, Offsetting Derivative Assets, Gross Amounts of Recognized Assets	27,600		27,600		75,500
Accounts receivable monetized gains-affiliate | Allocation To Limited Partner Only
Derivative [Line Items]
Affiliate Balances, Offsetting Derivative Assets, Gross Amounts of Recognized Assets	27,600		27,600		75,500
Long-term receivable monetized gains-affiliate
Derivative [Line Items]
Affiliate Balances, Offsetting Derivative Assets, Gross Amounts of Recognized Assets	3,200		3,200		15,100
Long-term receivable monetized gains-affiliate | Allocation To Limited Partner Only
Derivative [Line Items]
Affiliate Balances, Offsetting Derivative Assets, Gross Amounts of Recognized Assets	3,200		3,200		15,100
Put premiums payable-affiliate
Derivative [Line Items]
Affiliate Balances, Offsetting Derivative Liabilities, Gross Amounts Of Recognized Liabilities	6,100		6,100		6,000
Put premiums payable-affiliate | Allocation To Limited Partner Only
Derivative [Line Items]
Affiliate Balances, Offsetting Derivative Liabilities, Gross Amounts Of Recognized Liabilities	6,100		6,100		6,000
Long-term put premiums payable-affiliate
Derivative [Line Items]
Affiliate Balances, Offsetting Derivative Liabilities, Gross Amounts Of Recognized Liabilities	13,600		13,600		18,100
Long-term put premiums payable-affiliate | Allocation To Limited Partner Only
Derivative [Line Items]
Affiliate Balances, Offsetting Derivative Liabilities, Gross Amounts Of Recognized Liabilities	$ 13,600		$ 13,600		$ 18,100