Derivative Instruments and Hedging Activities (Details) (Derivatives designated as hedging instruments, USD $) In Thousands, unless otherwise specified	9 Months Ended
	Sep. 30, 2012	Dec. 31, 2011
Derivative Assets
Total derivatives		$ 31
Derivative Liabilities
Derivative financial instruments	(1,604)	(621)
Interest rate caps
Derivative Assets
Total derivatives		31
Interest rate caps one
Derivative Instruments and Hedging Activities
Notional Value	90,000
Index	one-month LIBOR
Interest rate caps one | Minimum
Derivative Instruments and Hedging Activities
Strike Rate (as a percent)	1.75%
Interest rate caps one | Maximum
Derivative Instruments and Hedging Activities
Strike Rate (as a percent)	2.00%
Interest rate caps two
Derivative Instruments and Hedging Activities
Notional Value	70,000
Index	one-month LIBOR
Interest rate caps two | Minimum
Derivative Instruments and Hedging Activities
Strike Rate (as a percent)	1.75%
Interest rate caps two | Maximum
Derivative Instruments and Hedging Activities
Strike Rate (as a percent)	2.00%
Interest rate swaps
Derivative Instruments and Hedging Activities
Notional Value	150,000
Index	one-month LIBOR
Strike Rate (as a percent)	0.79%
Derivative Liabilities
Derivative financial instruments	$ (1,604)	$ (621)