Fair Value (Details) (USD $)	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Derivative instruments and Hedging Activities
Hedging losses reclassified from accumulated other comprehensive income into earnings	$ 1,573,000	$ 1,391,000
Cash Flow Hedges
Derivative instruments and Hedging Activities
Number of derivative instruments held	3
Estimated hedging losses to be reclassified from accumulated other comprehensive loss into earnings within the next twelve months	5,493,000
Cash Flow Hedges | Interest Rate Caps
Derivative instruments and Hedging Activities
Notional balance	133,945,000
Weighted average interest rate (as a percent)	2.50%
Weighted average capped interest rate (as a percent)	4.90%
Non-Designated Hedges
Derivative instruments and Hedging Activities
Number of derivative instruments held	14
Unrecognized gain on derivatives		1,414,000
Non-Designated Hedges | Interest Rate Caps
Derivative instruments and Hedging Activities
Notional balance	$ 610,685,000
Weighted average interest rate (as a percent)	1.70%
Weighted average capped interest rate (as a percent)	5.90%