Risk Management and Fair Values (Reconciliation Of Changes In The Net Assets (Liabilities) For The Fair Value Of Derivatives Classified As Level 3 In The Fair Value Hierarchy) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011
Reconciliation of changes in the net assets (liabilities) for the fair value of derivatives classified as Level 3 in the fair value hierarchy
Balance as of Beginning of period	$ 312,000	$ 197,000
Unrealized gains from price changes	286,000	(62,000)
Unrealized gains on originations	1,000	(2,000)
Realized gains on settlements	(71,000)	(29,000)
Balance as of March 31	$ 528,000	$ 104,000