Fair Value (Details) (USD $)	9 Months Ended			1 Months Ended	9 Months Ended
	Sep. 30, 2012 Cash Flow Hedges derivative	Sep. 30, 2011 Cash Flow Hedges	Sep. 30, 2012 Cash Flow Hedges Interest Rate Caps	Sep. 30, 2012 Cash Flow Hedges Interest Rate Swaps	Sep. 30, 2011 Fair Value Hedges	Sep. 30, 2012 Non-Designated Hedges derivative	Sep. 30, 2012 Non-Designated Hedges Interest Rate Caps
Derivative instruments and Hedging Activities
Notional balance			$ 180,024,000	$ 215,000,000			$ 39,347,000
Weighted average interest rate (as a percent)			2.40%	4.60%			1.20%
Weighted average capped interest rate (as a percent)			5.30%				7.40%
Number of derivative instruments held	5					3
Payment for settlement of forward starting interest rate swap agreement				54,930,000
Amount of increase in comprehensive loss to adjust hedging derivatives	23,767,000	79,691,000
Estimated hedging losses to be reclassified from accumulated other comprehensive loss into earnings within the next twelve months	5,493,000
Fair value hedge derivative fair value decrease					$ 1,324,000