Equity (Details) $ / shares in Units, shares in Thousands, $ in Thousands				1 Months Ended	3 Months Ended		6 Months Ended
	Jul. 30, 2015 $ / shares	Apr. 30, 2015 $ / shares	Jan. 29, 2015 $ / shares	Jun. 30, 2015 USD ($) item	Jun. 30, 2015 USD ($) item $ / shares	Jun. 30, 2014 $ / shares	Jun. 30, 2015 USD ($) item $ / shares shares	Jun. 30, 2014 USD ($) $ / shares shares	Dec. 31, 2014 USD ($)
Equity
Common Stock, Dividends, Per Share, Declared | $ / shares	$ 0.565	$ 0.565	$ 0.565		$ 0.565	$ 0.545	$ 1.13	$ 1.09
Company's common stock issuances
Repurchase of common stock							$ 7,690	$ 11,086
Accumulated Other Comprehensive Loss
Cumulative foreign currency translation adjustment				$ (19,254)	$ (19,254)		(19,254)		$ (10,747)
Unrealized losses on cash flow hedges, net				(9,478)	(9,478)		(9,478)		(9,624)
Supplemental Executive Retirement Plan minimum liability				(3,399)	(3,399)		(3,399)		(3,537)
Unrealized gains on available for sale securities				16	16		16		13
Total accumulated other comprehensive loss				(32,115)	(32,115)		(32,115)		(23,895)
Noncontrolling interests
DownREIT unit, carrying value				186,343	$ 186,343		$ 186,343		$ 188,588
Maximum sales under equity offering program				$ 750,000
Common Stock
Company's common stock issuances
Dividend Reinvestment and Stock Purchase Plan (in shares) | shares							1,645	1,386
Conversion of DownREIT units (in shares) | shares							70	2
Exercise of stock options (in shares) | shares							817	111
Vesting of restricted stock units (in shares) | shares							379	567
Repurchase of common stock							$ 171	$ 284
Noncontrolling Interests
Noncontrolling interests
Non-managing members DownREIT units outstanding | item				4,000,000	4,000,000		4,000,000
Number of DownREIT LLCs | item				5	5		5
DownREIT unit, carrying value				$ 186,000	$ 186,000		$ 186,000
DownREIT unit, fair value				$ 219,000	$ 219,000		$ 219,000