Derivatives Derivatives (Schedule of Derivative Instruments, Gain (Loss) in Statement of Operations) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Derivative Instruments, Gain (Loss) [Line Items]
Gain (loss) on derivatives not designated as hedges and hedge ineffectiveness, net	$ 16,344	$ 1,387	$ 10,420	$ (606)
Not Designated as Hedging Instrument [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Realized gains (losses) on derivatives not designated as hedges	(181)	0	859	0
Unrealized gains on derivatives not designated as hedges	14,808	0	9,193	0
Designated as Hedging Instrument [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Unrealized gains (losses) on ineffectiveness of cash flow hedges	$ 1,717	$ 1,387	$ 368	$ (606)