Notes Payable and Unsecured Credit Facilities (Details) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2016	Dec. 31, 2015
Maturities of Long-term Debt [Abstract]
Long-term Debt, Maturities, Repayments of Principal, Remainder of Fiscal Year	$ 18,756
2017	423,076
2018	62,461
2019	275,130
2020	237,997
Beyond 5 Years	820,602
Unamortized debt (discounts) premiums, net	(2,722)
Long-term Debt	$ 1,835,300	$ 1,864,285
Mortgages [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Effective Percentage	3.696%
Maturities of Long-term Debt [Abstract]
Long-term Debt	$ 445,793	475,214
Notes Payable to Banks [Member]
Maturities of Long-term Debt [Abstract]
Long-term Debt	1,670,750	1,699,771
Unsecured Debt [Member]
Debt Instrument [Line Items]
Total credit facilities	164,550	164,514
Maturities of Long-term Debt [Abstract]
Long-term Debt	1,190,803	1,190,403
Line of Credit [Member] \| Unsecured Debt [Member]
Debt Instrument [Line Items]
Total credit facilities	0	0
Term Loan [Member] \| Unsecured Debt [Member]
Debt Instrument [Line Items]
Total credit facilities	$ 164,550	164,514
Construction Loans [Member] \| Variable Income Interest Rate [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate Terms	1 month LIBOR plus 150 basis points
Mortgages [Member]
Debt Instrument [Line Items]
Repayments of Debt	$ 27,300
Scheduled Principal Payments [Member] \| Mortgages [Member]
Maturities of Long-term Debt [Abstract]
Long-term Debt, Maturities, Repayments of Principal, Remainder of Fiscal Year	4,595
2017	5,778
2018	5,103
2019	4,130
2020	3,986
Beyond 5 Years	12,347
Unamortized debt (discounts) premiums, net	0
Long-term Debt	35,939
Mortgage Loan Maturities [Member] \| Mortgages [Member]
Maturities of Long-term Debt [Abstract]
Long-term Debt, Maturities, Repayments of Principal, Remainder of Fiscal Year	14,161
2017	117,298
2018	57,358
2019	106,000
2020	84,011
Beyond 5 Years	58,255
Unamortized debt (discounts) premiums, net	6,925
Long-term Debt	444,008
Unsecured Maturities [Member] \| Unsecured Debt [Member]
Maturities of Long-term Debt [Abstract]
Long-term Debt, Maturities, Repayments of Principal, Remainder of Fiscal Year	0
2017	300,000
2018	0
2019	165,000
2020	150,000
Beyond 5 Years	750,000
Unamortized debt (discounts) premiums, net	(9,647)
Long-term Debt	1,355,353
London Interbank Offered Rate (LIBOR) [Member] \| Mortgages [Member]
Maturities of Long-term Debt [Abstract]
Long-term Debt	$ 34,154	$ 34,154

Effective interest rate for the funds borrowed under the debt agreement considering interest compounding and original issue discount or premium.

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-Name Accounting Standards Codification
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