Derivative Financial Instruments - Floating-to-Fixed Interest Rate Swaps (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Derivative [Line Items]
Notional Amount	$ 496,642	$ 513,208
Interest rate swaps
Derivative [Line Items]
Notional Amount	246,642
Not Designated as Hedging Instrument
Derivative [Line Items]
Notional Amount	350,000	450,000
Not Designated as Hedging Instrument | Interest rate swaps
Derivative [Line Items]
Notional Amount	100,000	100,000
Not Designated as Hedging Instrument | Senior Unsecured Term Loan 2.00% | Interest rate swaps
Derivative [Line Items]
Notional Amount	$ 50,000
Fixed rate interest rate swap	2.00%
Effective interest rate	3.45%
Not Designated as Hedging Instrument | Senior Unsecured Term Loan 2.78% | Interest rate swaps
Derivative [Line Items]
Notional Amount	$ 50,000
Fixed rate interest rate swap	2.78%
Effective interest rate	4.23%
Designated as Hedging Instrument | Interest rate swaps
Derivative [Line Items]
Notional Amount	$ 146,642	$ 63,208
Designated as Hedging Instrument | Johns Hopkins Village | Interest rate swaps
Derivative [Line Items]
Notional Amount	$ 51,800
Fixed rate interest rate swap	2.94%
Effective interest rate	4.19%
Designated as Hedging Instrument | Senior Unsecured Term Loan 3.02% | Interest rate swaps
Derivative [Line Items]
Notional Amount	$ 10,500
Fixed rate interest rate swap	3.02%
Effective interest rate	4.47%
Designated as Hedging Instrument | 249 Central Park Retail, Fountain Plaza Retail, And South Retail | Interest rate swaps
Derivative [Line Items]
Notional Amount	$ 34,342
Fixed rate interest rate swap	2.25%
Effective interest rate	3.85%
Designated as Hedging Instrument | Senior Unsecured Term Loan 2.26% | Interest rate swaps
Derivative [Line Items]
Notional Amount	$ 50,000
Fixed rate interest rate swap	2.26%
Effective interest rate	3.71%