Notes Payable and Unsecured Credit Facilities (Details) (USD $)								6 Months Ended														0 Months Ended	6 Months Ended
	Jun. 30, 2013	Dec. 31, 2012	Jun. 30, 2013 Scheduled Principal Payments [Member]	Jun. 30, 2013 Mortgage Loan Maturities [Member]	Jun. 30, 2013 Unsecured Maturities [Member]		Jun. 30, 2013 Long-term Debt [Member]	Jun. 30, 2013 Line of Credit [Member]	Dec. 31, 2012 Line of Credit [Member]	Jun. 30, 2013 Term Loan - Unsecured [Member]	Dec. 31, 2012 Term Loan - Unsecured [Member]	Jun. 30, 2013 Notes Payable to Banks [Member]	Dec. 31, 2012 Notes Payable to Banks [Member]	Jun. 30, 2013 Fixed Rate Mortgage Loans [Member]	Dec. 31, 2012 Fixed Rate Mortgage Loans [Member]	Jun. 30, 2013 Variable Rate Mortgage Loans [Member]	Dec. 31, 2012 Variable Rate Mortgage Loans [Member]	Jun. 30, 2013 Fixed Rate Unsecured Loans [Member]	Dec. 31, 2012 Fixed Rate Unsecured Loans [Member]	Jun. 30, 2013 Unsecured Credit Facilities [Member]	Dec. 31, 2012 Unsecured Credit Facilities [Member]	May 01, 2013 Consolidated Entities [Member] Fixed Rate Mortgage Loans [Member] Seven Point One Percent Mortgage Maturing May 1, 2013 [Member]	Jun. 30, 2013 Consolidated Entities [Member] Fixed Rate Mortgage Loans [Member] 3.3% Mortgage Maturing April 1, 2020 [Member]	Jun. 30, 2013 Hilltop Village [Member] Consolidated Entities [Member] Fixed Rate Mortgage Loans [Member]	Jun. 30, 2013 Hilltop Village [Member] Consolidated Entities [Member] Fixed Rate Mortgage Loans [Member] Five Point Six Percent Mortgage Maturing April 6, 2016 [Member]	Jun. 30, 2013 Net increase/decrease [Member] Fixed Rate Mortgage Loans [Member]
Debt Instrument [Line Items]
Unsecured Line of Credit, Amount Outstanding								$ 45,000,000
Line of Credit Facility, Maximum Borrowing Capacity								800,000,000
Debt Instrument, Increase, Additional Borrowings																							8,250,000
Mortgage loans assumed for the acquisition of real estate																								7,500,000	7,500,000
Debt Instrument, Interest Rate, Stated Percentage																						10.00%	0.00%		6.00%
Long-term Debt, Amount Outstanding																						16,300,000				(4,800,000)
Maturities of Long-term Debt [Abstract]
2013			3,877,000	0	0	[1]	3,877,000
2014			7,383,000	26,853,000	150,000,000	[1]	184,236,000
2015			5,747,000	62,435,000	350,000,000	[1]	418,182,000
2016			5,487,000	21,661,000	125,000,000	[1]	152,148,000
2017			4,584,000	84,593,000	400,000,000	[1]	489,177,000
Beyond 5 Years			20,021,000	220,993,000	400,000,000	[1]	641,014,000
Unamortized debt (discounts) premiums, net			0	5,346,000	(1,856,000)	[1]	3,490,000
Long-term Debt, Amount Outstanding	$ 1,892,124,000	$ 1,941,891,000	$ 47,099,000	$ 421,881,000	$ 1,423,144,000	[1]	$ 1,892,124,000	$ 25,000,000	$ 70,000,000	$ 100,000,000	$ 100,000,000	$ 1,767,124,000	$ 1,771,891,000	$ 457,071,000	$ 461,914,000	$ 11,909,000	$ 12,041,000	$ 1,298,144,000	$ 1,297,936,000	$ 125,000,000	$ 170,000,000

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