Equity (Details) (USD $) Share data in Thousands, except Per Share data, unless otherwise specified	0 Months Ended		3 Months Ended
	Apr. 30, 2015	Jan. 29, 2015	Mar. 31, 2015	Mar. 31, 2014	Dec. 31, 2014
Equity
Dividends declared per common share (in dollars per share)	$ 0.565	$ 0.565	$ 0.565	$ 0.545
Company's common stock issuances
Repurchase of common stock			$ 6,096,000	$ 8,068,000
Accumulated Other Comprehensive Loss
Cumulative foreign currency translation adjustment			(17,710,000)		(10,747,000)
Unrealized losses on cash flow hedges, net			(7,291,000)		(9,624,000)
Supplemental Executive Retirement Plan minimum liability			(3,468,000)		(3,537,000)
Unrealized gains on available for sale securities			8,000		13,000
Total accumulated other comprehensive loss			(28,461,000)		(23,895,000)
Noncontrolling interests
DownREIT unit, carrying value			186,979,000		188,588,000
Common Stock
Company's common stock issuances
Dividend Reinvestment and Stock Purchase Plan (in shares)			829	875
Conversion of DownREIT units (in shares)			38	2
Exercise of stock options (in shares)			811	4
Vesting of restricted stock units (in shares)			288	411
Repurchase of common stock			128,000	208,000
Noncontrolling Interests
Noncontrolling interests
Non-managing members DownREIT units outstanding			4,000,000
Number of DownREIT LLCs			5
DownREIT unit, carrying value			187,000,000
DownREIT unit, fair value			$ 261,000,000