Other $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2015 USD ($) shares	Dec. 31, 2014 USD ($) $ / shares shares	Dec. 31, 2013 USD ($) $ / shares shares
Stock Issued During Period, Shares, New Issues | shares	0	0	34,468,085
Acquisition of Archstone Common Shares Issued	$ 0	$ 0	$ 1,929,868
Additional Common Shares Authorized | shares	13,000,000
Stock Repurchase Program, Number of Shares Authorized to be Repurchased | shares	13,000,000
Stock Repurchase Program, Remaining Number of Shares Authorized to be Repurchased | shares	12,968,760
Stock Repurchased and Retired During Period, Shares | shares	0	31,240	0
Treasury Stock Acquired, Average Cost Per Share | $ / shares		$ 56.87
OP units repurchased and retired	$ 0	$ 1,777	$ 0
Partially Owned Properties Acquired Properties		1
Partially Owned Units Acquired Units		268
Change in Paid In Capital		$ 2,300
Reduction In Partially Owned Properties		2,200
Reduction In Other Liabilities		1,000
Other Liabilities	366,387	389,915
Partner Buyout [Member]
Purchase Price, Business Acquisition, Cost of Acquired Entity		$ 5,500
Archstone Transaction [Member]
Stock Issued During Period, Shares, New Issues | shares			34,468,085
Acquisition of Archstone Common Shares Issued			$ 1,900,000
Average Price Per Common Share Issued | $ / shares			$ 55.99
Series P [Domain]
Preferred Stock Preference Units Dividend Rate Percentage		3.00%
Business Acquisition, Percentage of Voting Interests Acquired		95.00%
ERPOP [Member]
Acquisition of Archstone Common Shares Issued	0	$ 0	$ 1,929,868
Stock Repurchased and Retired During Period, Shares | shares		31,240
OP units repurchased and retired	0	$ 1,777	$ 0
Other Liabilities	$ 366,387	389,915
ERPOP [Member] | Archstone Transaction [Member]
Units Issued During Period New Issues | shares			34,468,085
Series P [Domain]
Other Liabilities		$ 18,400
NONCONTROLLING INTERESTS – PARTIALLY OWNED PROPERTIES
Land parcels acquired		1