Notes Payable and Unsecured Line of Credit Notes Payable and Unsecured Line of Credit (Details) (USD $)			9 Months Ended			9 Months Ended												9 Months Ended		3 Months Ended	9 Months Ended		9 Months Ended				3 Months Ended	9 Months Ended		3 Months Ended		9 Months Ended
	Sep. 30, 2011	Dec. 31, 2010	Sep. 30, 2011 Partnership Interest [Member]	Sep. 30, 2010 Partnership Interest [Member]	Dec. 31, 2010 Partnership Interest [Member]	Sep. 30, 2011 Partnership Interest [Member] Secured Debt [Member]	Sep. 30, 2011 Parent Company [Member]	Sep. 30, 2010 Parent Company [Member]	Dec. 31, 2010 Parent Company [Member]	Sep. 30, 2011 Scheduled Principal Payments [Member]	Sep. 30, 2011 Mortgage Loan Maturities [Member]	Sep. 30, 2011 Unsecured Maturities [Member]		Sep. 30, 2011 Notes Payable to Banks [Member]	Dec. 31, 2010 Notes Payable to Banks [Member]	Sep. 30, 2011 Fixed Rate Unsecured Loans [Member]	Dec. 31, 2010 Fixed Rate Unsecured Loans [Member]	Sep. 30, 2011 Fixed Rate Mortgage Loans [Member]	Dec. 31, 2010 Fixed Rate Mortgage Loans [Member]	Mar. 31, 2011 Unsecured Debt [Member]	Sep. 30, 2011 Unsecured Debt [Member]	Dec. 31, 2010 Unsecured Debt [Member]	Sep. 30, 2011 Unsecured Debt [Member] General Loan [Member]	Sep. 30, 2011 Unsecured Debt [Member] Construction Loans [Member]	Sep. 30, 2011 Secured Debt [Member]	Dec. 31, 2010 Line of Credit [Member]	Sep. 30, 2011 Line of Credit [Member] Line of Credit Facility - Unsecured [Member]	Sep. 30, 2011 Line of Credit [Member] Line of Credit Facility - Unsecured [Member]	Dec. 31, 2010 Line of Credit [Member] Line of Credit Facility - Unsecured [Member]	Mar. 31, 2011 Line of Credit [Member] Line of Credit Facility - Revolving [Member]	Feb. 28, 2011 Line of Credit [Member] Line of Credit Facility - Revolving [Member]	Sep. 30, 2011 Variable Income Interest Rate [Member] Construction Loans [Member]
Debt Instrument [Line Items]
Secured Debt, Percent Guaranteed by Parent Company						.1279
Debt Instrument, Maturity Date Range, End																					2021				2028
Debt Instrument, Interest Rate, Stated Percentage Rate Range, Minimum																		5.22%			4.80%
Debt Instrument, Interest Rate, Stated Percentage Rate Range, Maximum																		8.40%			7.25%
Debt, Weighted Average Interest Rate																		6.45%			5.61%
Mortgage Loans on Real Estate, Carrying Amount of Mortgages																							$ 3,800,000	$ 8,900,000
Debt Instrument, Interest Rate Terms																					7.95% ten-year senior		variable interest rate equal to LIBOR plus 380 basis points									variable interest rate of LIBOR plus 160 basis points
Debt Instrument, Maturity Date																				Jan. 31, 2011	Jan. 18, 2011		Oct. 01, 2014	Sep. 01, 2014
Repayments of Unsecured Debt			161,691,000	130,445,000			161,691,000	130,445,000													161,700,000
Line of Credit Facility, Unsecured, Annual Facility Fee																												annual facility fee of 25 basis points
Line of Credit Facility, Unsecured, Interest Rate Description																											variable interest rate of LIBOR plus 125 basis points
Line of Credit Facility, Revolving, Maximum Borrowing Capacity																											600,000,000	600,000,000			113,800,000
Line of Credit Facility, Revolving, Expiration Date																												September 2015, and includes one, one year extension option		February 2011
Long-term Debt, Amount Outstanding	2,050,340,000	2,094,469,000								56,749,000	398,810,000	1,594,781,000	[1]	1,965,340,000	2,084,469,000	1,509,781,000	1,671,129,000	442,860,000	402,151,000		12,699,000	11,189,000
Line of Credit Facility, Maximum Increase Allowed to Borrowing Capacity																											1,000,000,000	1,000,000,000
Unsecured Line of Credit, Amount Outstanding			85,000,000		10,000,000		85,000,000		10,000,000																	0	85,000,000	85,000,000	10,000,000
Maturities of Long-term Debt [Abstract]
2011	21,757,000									1,757,000	0	20,000,000	[1]
2012	199,375,000									6,998,000	0	192,377,000	[1]
2013	23,335,000									6,995,000	16,340,000	0	[1]
2014	186,224,000									6,481,000	29,743,000	150,000,000	[1]
2015	486,483,000									5,170,000	46,313,000	435,000,000	[1]
Beyond 5 Years	1,131,555,000									29,348,000	302,207,000	800,000,000	[1]
Unamortized debt discounts (premiums)	1,611,000									0	4,207,000	(2,596,000)	[1]
Long-term Debt, Amount Outstanding	$ 2,050,340,000	$ 2,094,469,000								$ 56,749,000	$ 398,810,000	$ 1,594,781,000	[1]	$ 1,965,340,000	$ 2,084,469,000	$ 1,509,781,000	$ 1,671,129,000	$ 442,860,000	$ 402,151,000		$ 12,699,000	$ 11,189,000

[1] Includes unsecured public debt and the Line. The Line is included in 2015 maturities and matures in September 2015.