Financial Instruments (Changes in Level 3 Inputs) (Details) (USD $)	3 Months Ended	9 Months Ended
	Sep. 30, 2012	Sep. 30, 2012
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Hypothetical change to estimated future cash flows attributable to commodity price swaps, percent	10.00%
Estimated change in fair value resulting from hypothetical percentage change in future cash flows attributable to commodity price swaps		$ 4,000,000
Commodity Contract [Member] | Level 3 [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance, January 1, 2012	119,461,000	31,616,000
Unrealized losses included in other comprehensive income	(192,446,000)	(158,893,000)
Settlements	44,937,000	99,229,000
Ending balance, March 31, 2012	(28,048,000)	$ (28,048,000)