Derivative Instruments (Schedule Of Derivative Instruments) (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Realized gain (loss) on derivative instruments, net	$ 41,122	$ 35,452	$ 33,218
Unrealized gain (loss) on derivative instruments, net	(9,751)	12,971	14,564
Gain (loss) on derivative instruments, net	$ 31,371	$ 48,423	$ 47,782