Fair Value Measurements (Assets and Liabilities Measured at Fair Value on Recurring Basis Using Significant Unobservable Inputs (Level 3), Reconciliation) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Fair Value Measurements [Abstract]
Balance at beginning of period	$ (27,958)	$ 106,222	$ (115)	$ 182,119
Total gains (losses): Included in earnings	4,617	53,465	(22,131)	177,201
Total gains or losses (realized/unrealized): Included in other comprehensive income		(57,614)		(135,055)
Purchases, issuances, and settlements:
Purchases
Issuances
Settlements	(2,020)	(55,112)	(3,115)	(177,304)
Balance at end of period	(25,361)	46,961	(25,361)	46,961
Change in gains (losses) included in earnings relating to derivatives still held as of September 30	$ 2,597	$ (1,647)	$ (25,246)	$ (103)