Notes Payable and Unsecured Credit Facilities (Details) - USD ($) $ in Thousands			6 Months Ended
	Jan. 05, 2022	Jul. 07, 2016	Jun. 30, 2016	Jun. 30, 2015	Jul. 13, 2016	Dec. 31, 2015
Debt Instrument [Line Items]
Document Period End Date			Jun. 30, 2016
Maturities of Long-term Debt [Abstract]
Long-term Debt, Maturities, Repayments of Principal, Remainder of Fiscal Year			$ 2,963
2017			423,076
Long-term Debt, Maturities, Repayments of Principal in Year Three			62,461
2019			420,393
2020			238,360
Beyond 5 Years			839,976
Unamortized debt (discounts) premiums, net			(3,013)
Long-term Debt			1,984,216			$ 1,864,285
Mortgages [Member]
Maturities of Long-term Debt [Abstract]
Long-term Debt			429,273			475,214
Notes Payable to Banks [Member]
Maturities of Long-term Debt [Abstract]
Long-term Debt			1,674,631			1,699,771
Unsecured Debt [Member]
Debt Instrument [Line Items]
Total credit facilities			309,585			164,514
Maturities of Long-term Debt [Abstract]
Long-term Debt			1,191,204			1,190,403
Line of Credit [Member] | Unsecured Debt [Member]
Debt Instrument [Line Items]
Total credit facilities			145,000			0
Term Loan [Member] | Unsecured Debt [Member]
Debt Instrument [Line Items]
Total credit facilities			164,585			164,514
Parent Company [Member]
Debt Instrument [Line Items]
Repayments of Notes Payable			$ 41,584	$ 76,027
Construction Loans [Member] | Variable Income Interest Rate [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate Terms			one month LIBOR plus 150 basis points
Fellsway $28.1M, Swap fixed 3.696% [Member] | Mortgages [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Effective Percentage			3.696%
Blackrock $20M, Swap fixed 2.803% [Member] | Mortgages [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Effective Percentage			2.803%
Scheduled Principal Payments [Member] | Mortgages [Member]
Maturities of Long-term Debt [Abstract]
Long-term Debt, Maturities, Repayments of Principal, Remainder of Fiscal Year			$ 2,963
2017			5,778
Long-term Debt, Maturities, Repayments of Principal in Year Three			5,103
2019			4,393
2020			4,349
Beyond 5 Years			13,184
Unamortized debt (discounts) premiums, net			0
Long-term Debt			35,770
Mortgage Loan Maturities [Member] | Mortgages [Member]
Maturities of Long-term Debt [Abstract]
Long-term Debt, Maturities, Repayments of Principal, Remainder of Fiscal Year			0
2017			117,298
Long-term Debt, Maturities, Repayments of Principal in Year Three			57,358
2019			106,000
2020			84,011
Beyond 5 Years			76,792
Unamortized debt (discounts) premiums, net			6,198
Long-term Debt			447,657
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
Long-term Debt, Maturities, Repayments of Principal in Year Three			0
2019			310,000
2020			150,000
Beyond 5 Years			750,000
Unamortized debt (discounts) premiums, net			(9,211)
Long-term Debt			1,500,789
Subsequent Event [Member] | Unsecured Debt [Member]
Maturities of Long-term Debt [Abstract]
Debt Instrument, Interest Rate, Stated Percentage					5.875%
Notice of Repayment of Unsecured Debt Subsequent to Period End Date, Make-Whole Premium Costs					$ 13,200
Subsequent Event [Member] | Term Loan [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Increase in Borrowing Capacity		$ 100,000
Line of Credit Facility, Maximum Borrowing Capacity		$ 265,000
Line of Credit Facility, Expiration Date	Jan. 05, 2022
Line of Credit Facility, Interest Rate Description		LIBOR plus a ratings based margin of 0.95%
Line of Credit Facility, Interest Rate at Period End		2.00%
London Interbank Offered Rate (LIBOR) [Member] | Mortgages [Member]
Debt Instrument [Line Items]
Proceeds from Issuance of Long-term Debt			20,000
Maturities of Long-term Debt [Abstract]
Long-term Debt			54,154			$ 34,154
Derivative @ 2.196% 28.1M [Member]
Debt Instrument [Line Items]
Derivative, Notional Amount			28,100
Derivative @ 1.30250% 20.0M [Member]
Debt Instrument [Line Items]
Derivative, Notional Amount			$ 20,000