Notes and Bonds Payable (Details) $ in Thousands		3 Months Ended
	Apr. 10, 2019 USD ($) ft²	Mar. 31, 2019 USD ($) ft²	Dec. 31, 2018 USD ($)
Debt Instrument [Line Items]
Notes and bonds payable		$ 1,343,110	$ 1,345,984
Area of Real Estate Property | ft²		15,000,000.0
Line of Credit | Unsecured Credit Facility
Debt Instrument [Line Items]
Notes and bonds payable		$ 260,000	262,000
Effective interest rate (percent)		3.49%
Medium-term Notes | Unsecured Term Loan Facility, net of issuance costs (1)
Debt Instrument [Line Items]
Notes and bonds payable		$ 149,234	149,183
Effective interest rate (percent)		3.53%
Notional amount		$ 50,000
Derivative, fixed interest rate (percent)		2.46%
Basis spread on variable rate (percent)		1.10%
Senior Notes | Senior Notes due 2023, net of discount and issuance costs
Debt Instrument [Line Items]
Notes and bonds payable		$ 248,223	248,117
Effective interest rate (percent)		3.95%
Senior Notes | Senior Notes due 2025, net of discount and issuance costs (2)
Debt Instrument [Line Items]
Notes and bonds payable		$ 248,338	248,278
Effective interest rate (percent)		4.08%
Senior Notes | Senior Notes due 2028, net of discount and issuance costs
Debt Instrument [Line Items]
Notes and bonds payable		$ 295,309	295,198
Effective interest rate (percent)		3.84%
Mortgages | Mortgage notes payable, net of discounts and issuance costs and including premiums
Debt Instrument [Line Items]
Notes and bonds payable		$ 142,006	$ 143,208
Effective interest rate (percent)		4.79%
Interest Rate Swap | Medium-term Notes | Unsecured Term Loan Facility, net of issuance costs (1)
Debt Instrument [Line Items]
Notional amount		$ 25,000
Derivative, fixed interest rate (percent)		2.18%
Interest Rate Swap | Senior Notes | Senior Notes due 2025, net of discount and issuance costs (2)
Debt Instrument [Line Items]
Loss on forward starting interest rate swap agreement recognized in OCI		$ 1,700
Subsequent Event | Mortgages | Mortgage notes payable, net of discounts and issuance costs and including premiums
Debt Instrument [Line Items]
Effective interest rate (percent)	5.00%
Extinguishment of Debt, Amount	$ 8,900
Area of Real Estate Property | ft²	52,813