Transactions with Affiliates and Other Related Parties (Details) (USD $)	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011	Dec. 31, 2011
Related Party Transaction [Line Items]
Number of Affiliated Partnerships	21		21
General and administrative expense	$ 14,378,000	$ 19,509,000	$ 29,086,000	$ 33,382,000
Affiliated Partnerships [Member]
Related Party Transaction [Line Items]
Gas Marketing segment sales	100,000	500,000	200,000	700,000
Gas marketing segment cost of sales	100,000	400,000	200,000	600,000
Fair value of derivative assets payable	11,100,000		11,100,000		14,200,000
Fair value of derivative liabilities receivable	4,600,000		4,600,000		6,200,000
PDCM [Member]
Related Party Transaction [Line Items]
Gas Marketing segment sales	2,200,000	3,300,000	4,600,000	5,100,000
Gas marketing segment cost of sales	2,100,000	3,300,000	4,500,000	5,100,000
Operating and administrative services billed	3,000,000	2,200,000	6,200,000	4,500,000
Former Executive Officer [Member]
Related Party Transaction [Line Items]
Description of Postemployment Benefits		In connection with his resignation, in July 2011, Mr. McCullough and the Company executed a separation agreement whereby Mr. McCullough received those benefits to which he was entitled under Section 7(d) of his employment agreement, dated as of April 19, 2010, including without limitation separation compensation in the amount of $4.1 million, less required withholdings, his annual non-qualified deferred supplemental retirement benefit equal to $30,000 for each of the years 2012 through 2021 (not accelerated), less required withholdings, continued coverage under the Company’s group health plans at the Company’s cost for a period equal to the lesser of 18 months or such period ending as of the date Mr. McCullough is eligible to participate in another employer’s group health plan, immediate vesting of any unvested Company stock options, SARs and restricted stock and issuance of shares representing the vested portion of his 2009 performance share awards.
General and administrative expense		$ 6,700,000