Significant Transactions (Details) (USD $)	3 Months Ended	6 Months Ended
	Jun. 30, 2011	Jun. 30, 2011
Business Combination, Separately Recognized Transactions [Line Items]
Sale of Woodlawn, a 159-unit community	$ 16,000,000	$ 16,000,000
Gain on sale of Woodlawn, net of internal distribution costs	5,300,000
Amount invested in Santa Clara joint venture development project	9,300,000	9,300,000
Mortgage amount associated with Santa Clara joint venture development project	10,500,000	10,500,000
Santa Clara joint venture development project mortgage due date	April 2014	April 2014
Santa Clara joint venture development mortgage interest rate	5.00%	5.00%
Santa Clara joint venture development option amount to purchase partners interest during 2011	800,000	800,000
Santa Clara joint venture development additional information	The plans for this project are to entitle a portion of the site for 494 apartment units. The joint venture partner has an option to purchase the retail parcel upon obtaining entitlements. The site is currently improved with retail space that is 100% leased.	The plans for this project are to entitle a portion of the site for 494 apartment units. The joint venture partner has an option to purchase the retail parcel upon obtaining entitlements. The site is currently improved with retail space that is 100% leased.
West Dublin development site purchase price	5,000,000	5,000,000
West Dublin site additional information	The 309-unit development will consist of a five-story building over two levels of parking and will feature a mix of one and two bedroom units and lofts.	The 309-unit development will consist of a five-story building over two levels of parking and will feature a mix of one and two bedroom units and lofts.
Schedule Of Equity And Cost Method Investments [Line Items]
Joint venture structure	50/50	50/50
Percentage interest in joint venture	28.20%	28.20%
Subsequent Event [Line Items]
Number of common shares sold (in shares)	984,982
Proceeds from sale of common shares	130,200,000	168,592,000
Average price per share of common shares sold (dollars per share)	$ 133.80
Number of preferred shares issued (in shares)	2,950,000	2,950,000
Price per preferred share (dollars per share)	$ 25.00	$ 25.00
Preferred shares proceeds	71,400,000	71,400,000
Bellerive [Member]
Business Combination, Separately Recognized Transactions [Line Items]
Number of units acquired	63	63
Cost of acquired entity	27,000,000	27,000,000
Apartment communities in downtown Los Angeles [Member]
Schedule Of Equity And Cost Method Investments [Line Items]
Amount of investment	13,000,000	13,000,000
Return on investment (in hundredths)	10.00%	10.00%
Investment redemption period (in years)	5Y	5Y
Wesco I LLC [Member]
Schedule Of Equity And Cost Method Investments [Line Items]
Amount of investment	200,000,000	200,000,000
Joint venture structure	50/50	50/50
Line of credit amount	100,000,000	100,000,000
Line of credit interest rate	LIBOR + 2.3%
Arbors Parc Rose [Member]
Schedule Of Equity And Cost Method Investments [Line Items]
Number of units acquired	373	373
Cost of acquired entity	92,000,000	92,000,000
Mortgage loan amount	59,900,000	59,900,000
Mortgage loan interest rate	4.7%
Mortgage loan term description (in years)	10
Reveal community in Canoga Park of Los Angeles [Member]
Schedule Of Equity And Cost Method Investments [Line Items]
Number of units acquired	438	438
Cost of acquired entity	132,900,000	132,900,000
Mortgage loan amount	78,700,000	78,700,000
Mortgage loan interest rate	LIBOR + 1.9%
Mortgage loan term description (in years)	two years with two one year extensions
Cadence [Member]
Schedule Of Equity And Cost Method Investments [Line Items]
Percentage interest in joint venture	55.00%	55.00%
Cairns mortgage loan [Member]
Extinguishment of Debt [Line Items]
Loan pay-off amount	11,300,000
Loan interest rate term description	3.7%
San Marcos mortgage loans [Member]
Extinguishment of Debt [Line Items]
Loan pay-off amount	46,500,000
Loan interest rate term description	blended rate of 5.3%
Unsecured Bond [Member]
Debt Instrument [Line Items]
Unsecured bond issuance proceeds	115,000,000	115,000,000
Unsecured bonds $75 million [Member]
Debt Instrument [Line Items]
Unsecured bond issuance proceeds	40,000,000	40,000,000
Unsecured bond stated interest (in hundredths)	4.50%	4.50%
Unsecured bonds $40 million [Member]
Debt Instrument [Line Items]
Unsecured bond issuance proceeds	75,000,000	75,000,000
Unsecured bond stated interest (in hundredths)	4.90%	4.90%
Issuance of Equity [Member]
Subsequent Event [Line Items]
Number of common shares sold (in shares)	350,112
Proceeds from sale of common shares	48,300,000
Average price per share of common shares sold (dollars per share)	$ 139.64
Cumulative Redeemable Preferred Units 7.875% Series B [Member]
Subsequent Event [Line Items]
Liquidation value of redeemed preferred shares	80,000,000	80,000,000
Excess of cash paid to redeem preferred shares	1,000,000	1,000,000
7.8125% Series F Cumulative Redeemable Preferred Stock [Member]
Subsequent Event [Line Items]
Liquidation value of redeemed preferred shares	25,000,000	25,000,000
Excess of cash paid to redeem preferred shares	$ 900,000	$ 900,000