Disclosure of Fair Value of Financial Instruments (Details) - Fair Value, Inputs, Level 3 [Member] - USD ($) $ in Thousands	Jun. 30, 2016	Dec. 31, 2015
Estimate of Fair Value Measurement [Member] | Mortgage Loans
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term Debt, Fair Value	$ 300,180	$ 306,334
Estimate of Fair Value Measurement [Member] | Unsecured Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term Debt, Fair Value	2,733,980	2,616,395
Portion at Other than Fair Value Measurement [Member] | Mortgage Loans
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term Debt, Fair Value	284,892	307,908
Portion at Other than Fair Value Measurement [Member] | Unsecured Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term Debt, Fair Value	$ 2,581,663	$ 2,580,108