Notes Payable (Summary Of Indebtedness) (Details) (USD $)					9 Months Ended		9 Months Ended		9 Months Ended		9 Months Ended		9 Months Ended		9 Months Ended		9 Months Ended		9 Months Ended						9 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 01, 2014	Apr. 30, 2014	Dec. 31, 2013	Sep. 30, 2014 Tax Exempt Mortgage Note Due 2028 (1.25% floating rate) Secured Debt [Member]	Dec. 31, 2013 Tax Exempt Mortgage Note Due 2028 (1.25% floating rate) Secured Debt [Member]	Sep. 30, 2014 5.08% Notes Due 2015 [Member] Senior Unsecured Notes [Member]	Dec. 31, 2013 5.08% Notes Due 2015 [Member] Senior Unsecured Notes [Member]	Sep. 30, 2014 5.75% Notes Due 2017 [Member] Senior Unsecured Notes [Member]	Dec. 31, 2013 5.75% Notes Due 2017 [Member] Senior Unsecured Notes [Member]	Sep. 30, 2014 4.70% Notes Due 2021 [Member] Senior Unsecured Notes [Member]	Dec. 31, 2013 4.70% Notes Due 2021 [Member] Senior Unsecured Notes [Member]	Sep. 30, 2014 3.07% Notes Due 2022 [Member] Senior Unsecured Notes [Member]	Dec. 31, 2013 3.07% Notes Due 2022 [Member] Senior Unsecured Notes [Member]	Sep. 30, 2014 5.00% Notes Due 2023 [Member] Senior Unsecured Notes [Member]	Dec. 31, 2013 5.00% Notes Due 2023 [Member] Senior Unsecured Notes [Member]	Sep. 30, 2014 4.27% Notes Due 2024 [Member] Senior Unsecured Notes [Member]	Dec. 31, 2013 4.27% Notes Due 2024 [Member] Senior Unsecured Notes [Member]	Sep. 30, 2014 3.59% Notes Due 2024 [Member] Senior Unsecured Notes [Member]	Dec. 31, 2013 3.59% Notes Due 2024 [Member] Senior Unsecured Notes [Member]	Sep. 30, 2014 Secured Notes 0.95% to 5.63% Conventional Mortgage Notes Due 2018 to 2045 [Member] Secured Debt [Member]	Dec. 31, 2013 Secured Notes 0.95% to 5.63% Conventional Mortgage Notes Due 2018 to 2045 [Member] Secured Debt [Member]	Sep. 30, 2014 Secured Notes 0.95% Floating Rate [Member] Secured Debt [Member]	Dec. 31, 2013 Secured Notes 0.95% Floating Rate [Member] Secured Debt [Member]	Sep. 30, 2014 Minimum [Member] Secured Notes 0.95% to 5.63% Conventional Mortgage Notes Due 2018 to 2045 [Member] Secured Debt [Member]	Sep. 30, 2014 Minimum [Member] Secured Notes 0.95% Floating Rate [Member] Secured Debt [Member]	Sep. 30, 2014 Maximum [Member] Secured Notes 0.95% to 5.63% Conventional Mortgage Notes Due 2018 to 2045 [Member] Secured Debt [Member]
Unsecured notes payable	$ 1,837,621,000			$ 1,588,798,000			$ 249,900,000	$ 249,700,000	$ 246,500,000	$ 246,400,000	$ 248,900,000	$ 248,800,000	$ 346,900,000	$ 346,700,000	$ 247,800,000	$ 247,700,000	$ 249,500,000	$ 249,500,000	$ 248,100,000	$ 0
Total secured notes payable	906,328,000			941,968,000	35,100,000	36,300,000															871,200,000	905,700,000	175,000,000	175,000,000
Total notes payable	$ 2,743,900,000			$ 2,530,800,000
Notes payable, effective interest rate	3.59%	2.20%	6.00%		1.25%		5.08%		5.75%		4.70%		3.07%		5.00%		4.27%		3.59%						0.95%	0.95%	5.63%
Notes payable, maturity date					2028		2015		2017		2021		2022		2023		2024		2024						2018		2045