Schedule of Debt (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Debt Instrument [Line Items]
Long-term Debt	$ 3,678,465	$ 3,715,212
Fixed Rate Mortgage Loans [Member]
Debt Instrument [Line Items]
Debt, Weighted Average Contractual Interest Rate	4.50%
Debt, Weighted Average Effective Interest Rate	4.00%
Long-term Debt	$ 344,963	403,306
Unsecured Debt [Member]
Debt Instrument [Line Items]
Debt, Weighted Average Contractual Interest Rate	4.00%
Debt, Weighted Average Effective Interest Rate	4.40%
Long-term Debt	$ 2,522,514	2,475,322
Total credit facilities	683,970	708,734
Notes Payable to Banks [Member]
Debt Instrument [Line Items]
Long-term Debt	$ 2,994,495	3,006,478
Line of Credit [Member]
Debt Instrument [Line Items]
Debt, Weighted Average Contractual Interest Rate	3.40%
Debt, Weighted Average Effective Interest Rate	3.60%
Line of Credit [Member] | Unsecured Debt [Member]
Debt Instrument [Line Items]
Total credit facilities	$ 120,000	145,000
Term Loan [Member]
Debt Instrument [Line Items]
Debt, Weighted Average Contractual Interest Rate	2.40%
Debt, Weighted Average Effective Interest Rate	2.50%
Term Loan [Member] | Unsecured Debt [Member]
Debt Instrument [Line Items]
Total credit facilities	$ 563,970	563,734
London Interbank Offered Rate (LIBOR) [Member] | Variable Rate Mortgage Loans [Member]
Debt Instrument [Line Items]
Debt, Weighted Average Contractual Interest Rate	3.50%
Debt, Weighted Average Effective Interest Rate	3.60%
Long-term Debt	$ 127,018	$ 127,850