Derivative Financial Instruments - Floating-to-Fixed Interest Rate Swaps (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Derivative [Line Items]
Notional amount	$ 790,594	$ 496,642
Interest rate swaps
Derivative [Line Items]
Notional amount	340,594
Not designated as accounting hedges
Derivative [Line Items]
Notional amount	200,000	350,000
Not designated as accounting hedges | Interest rate swaps
Derivative [Line Items]
Notional amount	50,000	100,000
Not designated as accounting hedges | Senior Unsecured Term Loan 2.78% | Interest rate swaps
Derivative [Line Items]
Notional amount	$ 50,000
Fixed interest rate	2.78%
Effective interest rate	4.33%
Designated as accounting hedge | Interest rate swaps
Derivative [Line Items]
Notional amount	$ 290,594	$ 146,642
Designated as accounting hedge | John Hopkins Village | Interest rate swaps
Derivative [Line Items]
Notional amount	$ 51,101
Fixed interest rate	2.94%
Effective interest rate	4.19%
Designated as accounting hedge | Senior Unsecured Term Loan 3.02% | Interest rate swaps
Derivative [Line Items]
Notional amount	$ 10,500
Fixed interest rate	3.02%
Effective interest rate	4.57%
Designated as accounting hedge | 249 Central Park Retail, South Retail, and Fountain Plaza Retail | Interest rate swaps
Derivative [Line Items]
Notional amount	$ 33,993
Fixed interest rate	2.25%
Effective interest rate	3.85%
Designated as accounting hedge | Senior Unsecured Term Loan 2.26% | Interest rate swaps
Derivative [Line Items]
Notional amount	$ 50,000
Fixed interest rate	2.26%
Effective interest rate	3.81%
Designated as accounting hedge | Thames Street Wharf | Interest rate swaps
Derivative [Line Items]
Notional amount	$ 70,000
Fixed interest rate	0.51%
Effective interest rate	1.81%
Designated as accounting hedge | Senior Unsecured Term Loan 0.50%, Term Loan One | Interest rate swaps
Derivative [Line Items]
Notional amount	$ 25,000
Fixed interest rate	0.50%
Effective interest rate	2.05%
Designated as accounting hedge | Senior Unsecured Term Loan 0.50%, Term Loan Two | Interest rate swaps
Derivative [Line Items]
Notional amount	$ 25,000
Fixed interest rate	0.50%
Effective interest rate	2.05%
Designated as accounting hedge | Senior Unsecured Term Loan 0.55% | Interest rate swaps
Derivative [Line Items]
Notional amount	$ 25,000
Fixed interest rate	0.55%
Effective interest rate	2.10%