Notes and Bonds Payable (Details) - USD ($)		3 Months Ended		6 Months Ended
	Jun. 01, 2021	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020	May 31, 2021	Dec. 31, 2020
Debt Instrument [Line Items]
Notes and bonds payable		$ 1,614,479,000		$ 1,614,479,000			$ 1,602,769,000
Impact of settlement of forward-starting interest rate swap		807,000	$ 1,455,000	(2,043,000)	$ 15,386,000
Line of credit | $700 million Unsecured Credit Facility
Debt Instrument [Line Items]
Notes and bonds payable		$ 13,000,000		$ 13,000,000			0
Effective interest rate		1.00%		1.00%
Credit facility		$ 700,000,000		$ 700,000,000
Medium-term notes | $200 million Unsecured Term Loan due 2024, net of issuance costs
Debt Instrument [Line Items]
Notes and bonds payable		$ 199,348,000		$ 199,348,000			199,236,000
Effective interest rate		1.95%		1.95%
Term-loan facility		$ 200,000,000		$ 200,000,000
Medium-term notes | $150 million Unsecured Term Loan due 2026, net of issuance costs
Debt Instrument [Line Items]
Notes and bonds payable		$ 149,306,000		$ 149,306,000			149,479,000
Effective interest rate		2.48%		2.48%
Term-loan facility		$ 150,000,000		$ 150,000,000		$ 150,000,000
Payment of up front fees	$ 500,000
Capitalized up front fees	$ 200,000
Debt administration fee		$ 300,000
Medium-term notes | $150 million Unsecured Term Loan due 2026, net of issuance costs | London Interbank Offered Rate (LIBOR)
Debt Instrument [Line Items]
Effective interest rate		0.95%		0.95%		1.60%
Medium-term notes | $150 million Unsecured Term Loan due 2026, net of issuance costs | Minimum | London Interbank Offered Rate (LIBOR)
Debt Instrument [Line Items]
Effective interest rate	0.80%					1.45%
Medium-term notes | $150 million Unsecured Term Loan due 2026, net of issuance costs | Maximum | London Interbank Offered Rate (LIBOR)
Debt Instrument [Line Items]
Effective interest rate	1.60%					2.40%
Senior notes | Senior Notes due 2025, net of discount and issuance costs
Debt Instrument [Line Items]
Notes and bonds payable		$ 248,906,000		$ 248,906,000			248,776,000
Effective interest rate		4.08%		4.08%
Senior notes | Senior Notes due 2028, net of discount and issuance costs
Debt Instrument [Line Items]
Notes and bonds payable		$ 296,365,000		$ 296,365,000			296,123,000
Effective interest rate		3.84%		3.84%
Senior notes | Senior notes due 2030, net of discount and issuance costs
Debt Instrument [Line Items]
Notes and bonds payable		$ 296,640,000		$ 296,640,000			296,468,000
Effective interest rate		2.71%		2.71%
Senior notes | Senior Notes due 2031, net of discount and issuance costs
Debt Instrument [Line Items]
Notes and bonds payable		$ 295,149,000		$ 295,149,000			294,924,000
Effective interest rate		2.24%		2.24%
Mortgages | Mortgage notes payable, net of discounts and issuance costs and including premiums
Debt Instrument [Line Items]
Notes and bonds payable		$ 115,765,000		$ 115,765,000			$ 117,763,000
Effective interest rate		4.07%		4.07%
Interest rate swaps
Debt Instrument [Line Items]
Impact of settlement of forward-starting interest rate swap		$ 807,000	1,455,000	$ 2,043,000	(11,119,000)
Interest rate swaps | Medium-term notes | $200 million Unsecured Term Loan due 2024, net of issuance costs
Debt Instrument [Line Items]
Notional amount		$ 75,000,000.0		$ 75,000,000.0
Weighted average interest rate (percent)		2.37%		2.37%
Basis spread on variable rate				100.00%
Interest rate swaps | Medium-term notes | $150 million Unsecured Term Loan due 2026, net of issuance costs
Debt Instrument [Line Items]
Notional amount		$ 100,000,000.0		$ 100,000,000.0
Weighted average interest rate (percent)		2.23%		2.23%
Basis spread on variable rate				95.00%
Interest rate swaps | Senior notes | Senior Notes due 2025, net of discount and issuance costs
Debt Instrument [Line Items]
Impact of settlement of forward-starting interest rate swap				$ 1,700,000
Treasury lock
Debt Instrument [Line Items]
Impact of settlement of forward-starting interest rate swap		$ 0	$ 0	0	$ (4,267,000)
Treasury lock | Senior notes | Senior Notes due 2025, net of discount and issuance costs
Debt Instrument [Line Items]
Impact of settlement of forward-starting interest rate swap				$ 4,300,000