Fair Value Of Instruments (Estimated Fair Value And Carrying Amounts) (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013		Dec. 31, 2012
Estimated Fair Value [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Unsecured senior notes	$ 2,449,596	[1],[2]	$ 1,907,188	[1],[2]
Exchangeable senior debentures	364,449	[1]	446,476	[1]
Mortgage Loans	728,760	[1]	845,125	[1]
Long-term Debt	4,991,092		4,680,357
Carrying Value [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Unsecured senior notes	2,382,059	[1],[2]	1,738,221	[1],[2]
Exchangeable senior debentures	266,400	[1]	266,400	[1]
Mortgage Loans	683,651	[1]	792,376	[1]
Long-term Debt	4,780,397		4,278,565
Senior Notes [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Unamortized discount	15,381		11,779
Global Revolving Credit Facility [Member] | Estimated Fair Value [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Lines of credit	498,082	[3]	723,729	[3]
Global Revolving Credit Facility [Member] | Carrying Value [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Lines of credit	498,082	[3]	723,729	[3]
Unsecured Term Loan [Member] | Estimated Fair Value [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Lines of credit	950,205	[4]	757,839	[4]
Unsecured Term Loan [Member] | Carrying Value [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Lines of credit	$ 950,205	[4]	$ 757,839	[4]

[1] Valuations for our unsecured senior notes and mortgage loans are determined based on the expected future payments discounted at risk-adjusted rates. The 2015 Notes, 2020 Notes, 2021 Notes, 2022 Notes and 2025 Notes and exchangeable senior debentures are valued based on quoted market prices.

[2] The carrying value of the 2015 Notes, 2020 Notes, 2021 Notes, 2022 Notes and 2025 Notes are net of discount of $15,381 and $11,779 in the aggregate as of September 30, 2013 and December 31, 2012, respectively.

[3] The carrying value of our global revolving credit facility approximates estimated fair value, due to the variability of interest rates and the stability of our credit rating.

[4] The carrying value of our unsecured term loan approximates estimated fair value, due to the variability of interest rates and the stability of our credit rating.