Derivatives and Hedging Activities (Schedule of Derivative Instruments in Statement of Financial Position, Fair Value) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended	12 Months Ended
	Mar. 31, 2013	Dec. 31, 2012
Derivatives, Fair Value [Line Items]
Derivatives, at fair value	$ 5,012	$ 3,830
Derivative Liability, Fair Value, Amount Offset Against Collateral	0	0
Derivative, Net Liability Position, Aggregate Fair Value	5,012	3,830
Financial Instruments, Owned, at Fair Value	0	0
Derivative, Cash Received on Hedge	0	0
Cash Flow Hedging [Member] | Designated as Hedging Instrument [Member] | Derivative Financial Instruments, Liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivative, at fair value	(5,012)	(3,830)
Swap [Member] | Cash Flow Hedging [Member] | Designated as Hedging Instrument [Member] | Derivative Financial Instruments, Liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivatives, at fair value	5,012	3,830
Interest Rate Cap [Member] | Cash Flow Hedging [Member] | Designated as Hedging Instrument [Member] | Derivative Financial Instruments, Liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivative, at fair value	$ 0	$ 0