Risk Management and Use of Financial Instruments (Fair Values of Derivative Financial Instruments) (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Derivatives, Fair Value [Line Items]
Long Term Debt Maturities Repayments Of Principal	$ 2,599,465
Derivative, Gain (Loss) on Derivative, Net	0	(2,985)	0
Other Assets [Member]
Derivatives, Fair Value [Line Items]
Notional Amount	51,548	51,548
Fair value	767	(2,391)
Other Assets [Member] | Interest Rate Swap [Member] | Cash Flow Hedging [Member] | 3.300% Interest Rate Swap Maturing January 30, 2021 [Member]
Derivatives, Fair Value [Line Items]
Notional Amount	25,774	25,774
Derivative, Fixed Interest Rate	3.30%
Fair value	549	(1,262)
Other Assets [Member] | Interest Rate Swap [Member] | Cash Flow Hedging [Member] | 3.090% Interest Rate Swap Maturing October 30, 2019 [Member]
Derivatives, Fair Value [Line Items]
Notional Amount	25,774	25,774
Derivative, Fixed Interest Rate	3.09%
Fair value	218	(1,129)
Other Liabilities [Member]
Derivatives, Fair Value [Line Items]
Notional Amount	377,062	377,062
Fair value	(2,188)	(11,819)
Other Liabilities [Member] | Interest Rate Swap [Member] | Cash Flow Hedging [Member] | 3.623% Interest Rate Swap Maturing February 1, 2019 [Member]
Derivatives, Fair Value [Line Items]
Notional Amount	200,000	200,000
Derivative, Fixed Interest Rate	3.623%
Fair value	(545)	(8,859)
Other Liabilities [Member] | Interest Rate Swap [Member] | Cash Flow Hedging [Member] | 2.703% Interest Rate Swap Maturing February 1, 2016 [Member]
Derivatives, Fair Value [Line Items]
Notional Amount	77,000	77,000
Derivative, Fixed Interest Rate	2.703%
Fair value	(887)	(1,343)
Other Liabilities [Member] | Interest Rate Swap [Member] | Cash Flow Hedging [Member] | 2.470% Interest Rate Swap Maturing February 1, 2015 [Member]
Derivatives, Fair Value [Line Items]
Notional Amount	50,000	50,000
Derivative, Fixed Interest Rate	2.47%
Fair value	(283)	(458)
Other Liabilities [Member] | Interest Rate Swap [Member] | Cash Flow Hedging [Member] | 2.513% Interest Rate Swap Maturing May 1, 2015 [Member]
Derivatives, Fair Value [Line Items]
Notional Amount	23,000	23,000
Derivative, Fixed Interest Rate	2.513%
Fair value	(162)	(245)
Other Liabilities [Member] | Interest Rate Swap [Member] | Cash Flow Hedging [Member] | 2.750% Interest Rate Swap Maturing September 30, 2017 [Member]
Derivatives, Fair Value [Line Items]
Notional Amount	27,062	27,062
Derivative, Fixed Interest Rate	2.75%
Fair value	$ (311)	$ (914)