Derivatives and Hedging Activities (Schedule of Derivative Instruments in Statement of Financial Position, Fair Value) (Details) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
Derivatives, Fair Value [Line Items]
Interest rate swap assets	$ 0	$ 5,509
Interest rate swap liabilities	(15,350)	(7,384)
Interest Rate Swap [Member] | Not Designated as Hedging Instrument [Member] | Deferred Costs and Other Assets, Net [Member]
Derivatives, Fair Value [Line Items]
Interest rate swap assets	0	568
Interest Rate Swap [Member] | Not Designated as Hedging Instrument [Member] | Deferred Rent, Derivative and Other Liabilities [Member]
Derivatives, Fair Value [Line Items]
Interest rate swap liabilities	(474)	0
Cash Flow Hedging [Member] | Interest Rate Swap [Member] | Designated as Hedging Instrument [Member] | Deferred Costs and Other Assets, Net [Member]
Derivatives, Fair Value [Line Items]
Interest rate swap assets	0	4,941
Cash Flow Hedging [Member] | Interest Rate Swap [Member] | Designated as Hedging Instrument [Member] | Deferred Rent, Derivative and Other Liabilities [Member]
Derivatives, Fair Value [Line Items]
Interest rate swap liabilities	$ (14,876)	$ (7,384)