Derivatives Derivatives (Schedule of Derivative Instruments, Gain (Loss) in Statement of Income) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Derivative Instruments, Gain (Loss) [Line Items]
Loss on derivatives not designated as hedges and hedge ineffectiveness, net	$ (5,924)	$ (1,993)
Not Designated as Hedging Instrument [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Realized gains on derivatives not designated as hedges	1,040	0
Unrealized losses on derivatives not designated as hedges	(5,615)	0
Designated as Hedging Instrument [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Unrealized losses on ineffectiveness of cash flow hedges	$ (1,349)	$ (1,993)