Fair Value (Details) $ in Thousands		3 Months Ended		6 Months Ended
		Jun. 30, 2015 USD ($) derivative	Jun. 30, 2014 USD ($)	Jun. 30, 2015 USD ($) derivative	Jun. 30, 2014 USD ($)
Derivative instruments and Hedging Activities
Hedging losses reclassified from accumulated other comprehensive income into earnings		$ 1,427	$ 1,438	$ 2,992	$ 3,011
Estimated hedging losses to be reclassified from accumulated other comprehensive loss into earnings within the next twelve months		$ 5,493
Cash Flow Hedges
Derivative instruments and Hedging Activities
Weighted average interest rate (as a percent)	[1]	2.30%		2.30%
Number of derivative instruments held | derivative		1		1
Interest Rate Cap [Member] | Cash Flow Hedges
Derivative instruments and Hedging Activities
Notional balance		$ 37,138		$ 37,138
Weighted average capped interest rate (as a percent)		5.90%		5.90%
Not Designated as Hedging Instrument [Member]
Derivative instruments and Hedging Activities
Number of derivative instruments held | derivative		15		15
Not Designated as Hedging Instrument [Member] | Interest Rate Cap [Member]
Derivative instruments and Hedging Activities
Notional balance		$ 727,474		$ 727,474
Weighted average interest rate (as a percent)	[1]	1.90%		1.90%
Weighted average capped interest rate (as a percent)		5.80%		5.80%

[1] Represents the weighted average interest rate on the hedged debt.