Notes Payable (Narrative) (Details) $ in Thousands		1 Months Ended	3 Months Ended	12 Months Ended
		Aug. 31, 2022 USD ($)	Dec. 31, 2022 USD ($) yr	Dec. 31, 2022 USD ($) yr	Dec. 31, 2021 USD ($)	Dec. 31, 2020 USD ($)	Sep. 30, 2022 USD ($)	Apr. 01, 2022 USD ($)	Mar. 31, 2019 USD ($)
Debt Instrument, Unamortized Discount (Premium) and Debt Issuance Costs, Net			$ 18,000	$ 18,000	$ 19,600
Unsecured Debt			3,165,924	3,165,924	3,170,367
Total notes payable	[1]		3,680,900	3,680,900	3,170,400
Loss on early retirement of debt				0	0	$ 176
Available amount under unsecured credit facility			$ 1,100,000	$ 1,100,000
Weighted average interest rate on floating rate debt	[2]		4.00%	4.00%
Weighted average maturity of indebtedness (including unsecured credit facility and unsecured short-term borrowings) (in years) | yr			6.4	6.4
Repayments of Notes Payable				$ 350,000	0	$ 100,000
Secured Debt			$ 514,989	514,989	0
Debt Instrument, Unamortized Discount (Premium), Net								$ 2,400
Amortization of Debt Discount (Premium)			400
The Funds
Secured Debt								$ 514,600
Letter Of Credit [Member]
Maximum Ability to Issue Letters of Credit Under Unsecured Credit Facility			50,000	50,000
Outstanding balance under credit facility			14,200	14,200
Commercial Banks [Member] | Unsecured Credit Facility [Member]
Unsecured Debt			42,000	42,000	0
Senior Unsecured Notes [Member]
Unsecured Debt			2,784,100	2,784,100	3,130,500
Secured Debt [Member] | Minimum [Member] | The Funds
Notes payable, effective interest rate								2.47%
Secured Debt [Member] | Maximum [Member] | The Funds
Notes payable, effective interest rate								4.04%
secured notes payable | The Funds
Secured Debt								$ 514,600
Unsecured Credit Facility [Member]
Value not exceeding the amount available under the unsecured credit facility				600,000
Line of Credit Facility, Maximum Borrowing Capacity			$ 1,200,000	$ 1,200,000
Terms Of Bid Rate Loans				180 days
Line of Credit Facility, Increase (Decrease), Net		$ 300,000
Unsecured Credit Facility [Member] | March 2019 Credit Agreement
Line of Credit Facility, Maximum Borrowing Capacity									$ 900,000
Unsecured Credit Facility [Member] | Commercial Banks [Member]
Notes payable, effective interest rate			5.13%	5.13%
Floating Rate Notes Payable [Member]
Total notes payable	[3]		$ 566,900	$ 566,900	$ 39,900
Weighted average interest rate on floating rate debt			5.50%	5.50%	1.90%
5.31% Term loan Due 2024 | Commercial Banks [Member]
Unsecured Debt			$ 39,800	$ 39,800	$ 39,900
Debt Instrument, Maturity Date				Sep. 30, 2024
Notes payable, effective interest rate			5.31%	5.31%	1.85%
5.20% Term loan, due 2024 | Commercial Banks [Member]
Unsecured Debt			$ 300,000	$ 300,000	$ 0
Debt Instrument, Maturity Date				Aug. 29, 2025
Notes payable, effective interest rate			5.20%	5.20%
3.78% - 4.04% Conventional Mortgage Notes, due 2026 - 2028 | Secured Debt [Member]
Secured Debt			$ 291,200	$ 291,200	0
3.78% - 4.04% Conventional Mortgage Notes, due 2026 - 2028 | Secured Debt [Member] | Minimum [Member]
Debt Instrument, Maturity Date				Oct. 01, 2026
Notes payable, effective interest rate			3.78%	3.78%
3.78% - 4.04% Conventional Mortgage Notes, due 2026 - 2028 | Secured Debt [Member] | Maximum [Member]
Debt Instrument, Maturity Date				Apr. 01, 2028
Notes payable, effective interest rate			4.04%	4.04%
6.16% Variable Rate Notes, due 2026 | Secured Debt [Member]
Notes payable, effective interest rate			6.16%	6.16%
Secured Debt			$ 166,200	$ 166,200	0
6.16% Variable Rate Notes, due 2026 | Secured Debt [Member] | Minimum [Member]
Debt Instrument, Maturity Date				Apr. 01, 2026
6.16% Variable Rate Notes, due 2026 | Secured Debt [Member] | Maximum [Member]
Debt Instrument, Maturity Date				Oct. 01, 2026
6.49% Variable Rate Construction Note, due 2024 | Secured Debt [Member]
Debt Instrument, Maturity Date				Jun. 20, 2024
Notes payable, effective interest rate			6.49%	6.49%
Secured Debt			$ 18,900	$ 18,900	0
3.87% note, due 2028 | Secured Debt [Member]
Debt Instrument, Maturity Date				Jan. 01, 2028
Notes payable, effective interest rate			3.87%	3.87%
Secured Debt			$ 38,700	$ 38,700	0
3.15% Notes Due 2022 | Senior Unsecured Notes [Member]
Unsecured Debt			$ 0	$ 0	$ 349,300
Debt Instrument, Maturity Date				Dec. 15, 2022
Notes payable, effective interest rate			3.15%	3.15%	3.15%
Repayments of Notes Payable				$ 350,000
Term loan, due 2024 full value | Commercial Banks [Member]
Unsecured Debt							$ 40,000

[1] Unamortized debt discounts, debt issuance costs, and fair market value adjustments of $18.0 million and $19.6 million are included in senior unsecured notes payable as of December 31, 2022 and 2021, respectively.

[2] Includes the effects of the applicable settled forward interest rate swaps.

[3] Includes balances outstanding under our unsecured credit facility at December 31, 2022.