Schedule of Debt (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Debt Instrument [Line Items]
Long-term Debt	$ 3,683,738	$ 3,715,212
Fixed Rate Mortgage Loans [Member]
Debt Instrument [Line Items]
Long-term Debt	360,865	403,306
Notes Payable to Banks [Member]
Debt Instrument [Line Items]
Long-term Debt	3,009,886	3,006,478
Unsecured Debt [Member]
Debt Instrument [Line Items]
Total credit facilities	673,852	708,734
Long-term Debt	2,521,940	2,475,322
Line of Credit [Member] | Unsecured Debt [Member]
Debt Instrument [Line Items]
Total credit facilities	110,000	145,000
Term Loan [Member] | Unsecured Debt [Member]
Debt Instrument [Line Items]
Total credit facilities	563,852	563,734
London Interbank Offered Rate (LIBOR) [Member] | Variable Rate Mortgage Loans [Member]
Debt Instrument [Line Items]
Long-term Debt	$ 127,081	$ 127,850
Contractual Rate [Member] | Fixed Rate Mortgage Loans [Member]
Debt Instrument [Line Items]
Debt, Weighted Average Interest Rate	4.50%
Contractual Rate [Member] | Variable Rate Mortgage Loans [Member]
Debt Instrument [Line Items]
Debt, Weighted Average Interest Rate	3.50%
Contractual Rate [Member] | Unsecured Debt [Member]
Debt Instrument [Line Items]
Debt, Weighted Average Interest Rate	4.00%
Contractual Rate [Member] | Line of Credit [Member]
Debt Instrument [Line Items]
Debt, Weighted Average Interest Rate	3.50%
Contractual Rate [Member] | Term Loan [Member]
Debt Instrument [Line Items]
Debt, Weighted Average Interest Rate	2.40%
Effective Rate [Member] | Fixed Rate Mortgage Loans [Member]
Debt Instrument [Line Items]
Debt, Weighted Average Interest Rate	4.10%
Effective Rate [Member] | Variable Rate Mortgage Loans [Member]
Debt Instrument [Line Items]
Debt, Weighted Average Interest Rate	3.60%
Effective Rate [Member] | Unsecured Debt [Member]
Debt Instrument [Line Items]
Debt, Weighted Average Interest Rate	4.40%
Effective Rate [Member] | Line of Credit [Member]
Debt Instrument [Line Items]
Debt, Weighted Average Interest Rate	3.70%
Effective Rate [Member] | Term Loan [Member]
Debt Instrument [Line Items]
Debt, Weighted Average Interest Rate	2.50%