Schedule of Debt (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Debt Instrument [Line Items]
Long-term Debt	$ 3,887,268	$ 3,715,212
Fixed Rate Mortgage Loans [Member]
Debt Instrument [Line Items]
Debt, Weighted Average Contractual Interest Rate	4.40%
Debt, Weighted Average Effective Interest Rate	4.00%
Long-term Debt	$ 344,610	403,306
Unsecured Debt [Member]
Debt Instrument [Line Items]
Debt, Weighted Average Contractual Interest Rate	3.90%
Debt, Weighted Average Effective Interest Rate	4.20%
Long-term Debt	$ 2,944,076	2,475,322
Total credit facilities	449,309	708,734
Notes Payable to Banks [Member]
Debt Instrument [Line Items]
Long-term Debt	$ 3,437,959	3,006,478
Line of Credit [Member]
Debt Instrument [Line Items]
Debt, Weighted Average Contractual Interest Rate	3.10%
Debt, Weighted Average Effective Interest Rate	3.30%
Line of Credit [Member] | Unsecured Debt [Member]
Debt Instrument [Line Items]
Total credit facilities	$ 185,000	145,000
Term Loan [Member]
Debt Instrument [Line Items]
Debt, Weighted Average Contractual Interest Rate	2.00%
Debt, Weighted Average Effective Interest Rate	2.10%
Term Loan [Member] | Unsecured Debt [Member]
Debt Instrument [Line Items]
Total credit facilities	$ 264,309	563,734
London Interbank Offered Rate (LIBOR) [Member] | Variable Rate Mortgage Loans [Member]
Debt Instrument [Line Items]
Debt, Weighted Average Contractual Interest Rate	3.20%
Debt, Weighted Average Effective Interest Rate	3.40%
Long-term Debt	$ 149,273	$ 127,850