Disclosure of Fair Value of Financial Instruments (Details) (Fair Value, Inputs, Level 3 [Member], USD $) In Thousands, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013
Reported Value Measurement [Member] | Unsecured Debt [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term Debt, Fair Value	$ 2,708,668	$ 2,708,213
Reported Value Measurement [Member] | Mortgage Loans on Real Estate [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term Debt, Fair Value	537,338	545,306
Estimate of Fair Value Measurement [Member] | Unsecured Debt [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term Debt, Fair Value	2,850,123	2,764,831
Estimate of Fair Value Measurement [Member] | Mortgage Loans on Real Estate [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term Debt, Fair Value	$ 561,388	$ 573,944