Derivatives and Hedging Activities (Details) (USD $)	3 Months Ended							3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Mar. 31, 2013 Cash Flow Hedging [Member] Interest Rate Swap [Member]	Mar. 31, 2012 Cash Flow Hedging [Member] Interest Rate Swap [Member]	Mar. 31, 2013 Cash Flow Hedging [Member] Interest Rate Swap [Member] Interest Expense [Member]	Mar. 31, 2012 Cash Flow Hedging [Member] Interest Rate Swap [Member] Interest Expense [Member]	Mar. 31, 2013 Cash Flow Hedging [Member] Interest Rate Swap [Member] Designated as Hedging Instrument [Member]	Mar. 31, 2013 Cash Flow Hedging [Member] Interest Rate Swap [Member] Designated as Hedging Instrument [Member] Interest Expense [Member]	Mar. 31, 2013 Derivative Financial Instruments, Liabilities [Member] Cash Flow Hedging [Member] Designated as Hedging Instrument [Member] derivative	Dec. 31, 2012 Derivative Financial Instruments, Liabilities [Member] Cash Flow Hedging [Member] Designated as Hedging Instrument [Member] derivative	Mar. 31, 2013 Derivative Financial Instruments, Liabilities [Member] Interest Rate Cap [Member] Cash Flow Hedging [Member] Designated as Hedging Instrument [Member] derivative	Dec. 31, 2012 Derivative Financial Instruments, Liabilities [Member] Interest Rate Cap [Member] Cash Flow Hedging [Member] Designated as Hedging Instrument [Member] derivative
Derivatives, Fair Value [Line Items]
Assets Needed for Immediate Settlement, Aggregate Fair Value							$ 5,100,000
Interest Rate Derivative Liabilities, at Fair Value									5,012,000	3,830,000	0	0
Number of Interest Rate Derivatives Held									10	8	1	1
Designated derivatives, fair value adjustment	(1,177,000)	(603,000)	(1,859,000)	(689,000)
Derivative Instruments, Gain (Loss) Reclassification from Accumulated OCI to Income, Estimated Net Amount to be Transferred								4,700,000
Loss on derivative instruments	(5,000)	0			(682,000)	(86,000)
Derivative Instruments, Gain (Loss) Recognized in Income, Ineffective Portion and Amount Excluded from Effectiveness Testing, Net	(5,000)	0	0	0
Notional Amount of Interest Rate Derivatives									$ 717,590,000	$ 202,590,000	$ 50,000,000	$ 50,000,000