Derivatives and Hedging Activities (Schedule of Derivative Instruments in Statement of Financial Position, Fair Value) (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Derivatives, Fair Value [Line Items]
Derivative asset	$ 5,509	$ 9,189	[1]
Interest Rate Contract [Member] | Not Designated as Hedging Instrument [Member] | Deferred Costs and Other Assets, Net [Member]
Derivatives, Fair Value [Line Items]
Derivative asset	568	0
Series D Preferred Stock Embedded Derivative [Member] | Not Designated as Hedging Instrument [Member] | Deferred Rent, Derivative Liabilities and Other Liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivative liability	0	(16,736)
Cash Flow Hedging [Member] | Interest Rate Contract [Member] | Designated as Hedging Instrument [Member] | Deferred Costs and Other Assets, Net [Member]
Derivatives, Fair Value [Line Items]
Derivative asset	4,941	9,189
Cash Flow Hedging [Member] | Interest Rate Contract [Member] | Designated as Hedging Instrument [Member] | Derivative Liabilities, at Fair Value [Member]
Derivatives, Fair Value [Line Items]
Derivative liability	$ (7,384)	$ (1,719)

[1] December 31, 2013 line items have been broken out since the previously filed presentation to conform with current presentation and provide detailed balances relating to derivative assets, prepaid expenses, and deferred costs.