Notes Payable and Unsecured Credit Facilities (Details) (USD $)	3 Months Ended
	Mar. 31, 2015		Dec. 31, 2014
Debt Instrument [Line Items]
Document Period End Date	Mar. 31, 2015
Total debt outstanding	$ 1,994,727,000		$ 2,021,357,000
Document Fiscal Year Focus	2015
Fixed Rate Mortgage Loans [Member]
Debt Instrument [Line Items]
Debt, Weighted Average Interest Rate	5.20%
Total notes payable	460,885,000		518,993,000
Maturities of Long-term Debt [Abstract]
Long-term Debt, Amount Outstanding	460,885,000		518,993,000
Notes Payable to Banks [Member]
Debt Instrument [Line Items]
Total notes payable	1,889,727,000		1,946,357,000
Maturities of Long-term Debt [Abstract]
Long-term Debt, Amount Outstanding	1,889,727,000		1,946,357,000
Variable Rate Mortgage Loans [Member]
Debt Instrument [Line Items]
Debt, Weighted Average Interest Rate	1.30%
Total notes payable	31,190,000		29,839,000
Maturities of Long-term Debt [Abstract]
Long-term Debt, Amount Outstanding	31,190,000		29,839,000
Fixed Rate Unsecured Loans [Member]
Debt Instrument [Line Items]
Total notes payable	1,397,652,000		1,397,525,000
Maturities of Long-term Debt [Abstract]
Long-term Debt, Amount Outstanding	1,397,652,000		1,397,525,000
Unsecured Debt [Member]
Debt Instrument [Line Items]
Total credit facilities	105,000,000		75,000,000
Line of Credit [Member]
Debt Instrument [Line Items]
Proceeds from Lines of Credit	30,000,000
Borrowing capacity	800,000,000
Line of Credit [Member] | Unsecured Debt [Member]
Debt Instrument [Line Items]
Total credit facilities	30,000,000		0
Term Loan [Member] | Unsecured Debt [Member]
Debt Instrument [Line Items]
Total credit facilities	75,000,000		75,000,000
5.650% & 5.360% maturing in 2015 [Member]
Debt Instrument [Line Items]
Repayments of Debt	55,800,000
$165 mill Term Loan LIBOR plus 1.15, .20% unused fee [Member] | Term Loan [Member] | Unsecured Debt [Member]
Debt Instrument [Line Items]
Borrowing capacity	67.40
Consolidated Entities [Member] | 2.196 Fixed rate with interest rate swap LIBOR 1.5% Maturing 10/16/20 [Member] | Variable Rate Mortgage Loans [Member]
Debt Instrument [Line Items]
Proceeds from Construction Loans Payable	1,400,000
Scheduled Principal Payments [Member]
Debt Instrument [Line Items]
Total notes payable	46,801,000
Maturities of Long-term Debt [Abstract]
2015	4,724,000
2016	6,135,000
2017	5,399,000
2018	4,452,000
2019	3,443,000
Beyond 5 Years	22,648,000
Unamortized debt (discounts) premiums, net	0
Long-term Debt, Amount Outstanding	46,801,000
Mortgage Loan Maturities [Member]
Debt Instrument [Line Items]
Total notes payable	445,274,000
Maturities of Long-term Debt [Abstract]
2015	20,391,000
2016	41,442,000
2017	116,316,000
2018	57,358,000
2019	106,000,000
Beyond 5 Years	97,390,000
Unamortized debt (discounts) premiums, net	6,377,000
Long-term Debt, Amount Outstanding	445,274,000
Unsecured Maturities [Member]
Debt Instrument [Line Items]
Total notes payable	1,502,652,000	[1]
Maturities of Long-term Debt [Abstract]
2015	350,000,000	[1]
2016	30,000,000	[1]
2017	400,000,000	[1]
2018	0	[1]
2019	75,000,000	[1]
Beyond 5 Years	650,000,000	[1]
Unamortized debt (discounts) premiums, net	(2,348,000)	[1]
Long-term Debt, Amount Outstanding	1,502,652,000	[1]
Long-term Debt [Member]
Debt Instrument [Line Items]
Total notes payable	1,994,727,000
Maturities of Long-term Debt [Abstract]
2015	375,115,000
2016	77,577,000
2017	521,715,000
2018	61,810,000
2019	184,443,000
Beyond 5 Years	770,038,000
Unamortized debt (discounts) premiums, net	4,029,000
Long-term Debt, Amount Outstanding	$ 1,994,727,000

[1] Includes unsecured public debt and unsecured credit facilities.