Fair Value of Financial Instruments (Details) - Fair Value, Inputs, Level 3 [Member] - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Carrying Value [Member] | Unsecured Debt [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Mortgage Loans and Unsecured Notes Fair Value	$ 2,580,108	$ 2,498,021
Carrying Value [Member] | Mortgages [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Mortgage Loans and Unsecured Notes Fair Value	307,908	484,852
Estimate of Fair Value Measurement [Member] | Unsecured Debt [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Mortgage Loans and Unsecured Notes Fair Value	2,616,395	2,704,069
Estimate of Fair Value Measurement [Member] | Mortgages [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Mortgage Loans and Unsecured Notes Fair Value	$ 306,334	$ 501,231