Debt - Narrative (Details) $ in Millions	1 Months Ended	6 Months Ended
	Jul. 31, 2020 USD ($) loan	Jun. 30, 2020 USD ($)	Dec. 31, 2019 USD ($)
Mortgages Payable
Mortgages and Line of Credit Facility [Line Items]
Net carrying value of real estate collateralizing the mortgages payable		$ 1,600.0	$ 1,400.0
Mortgages Payable | Interest rate swaps and caps
Mortgages and Line of Credit Facility [Line Items]
Derivative, notional amount		945.4	$ 867.6
Credit Facility
Mortgages and Line of Credit Facility [Line Items]
Credit facility, maximum borrowing capacity		1,400.0
Credit Facility | Revolving Credit Facility
Mortgages and Line of Credit Facility [Line Items]
Credit facility, maximum borrowing capacity		1,000.0
Credit Facility | Tranche A-1 Term Loan
Mortgages and Line of Credit Facility [Line Items]
Credit facility, maximum borrowing capacity		200.0
Credit Facility | Tranche A-2 Term Loan
Mortgages and Line of Credit Facility [Line Items]
Credit facility, maximum borrowing capacity		200.0
4747 Bethesda Avenue | Mortgages Payable
Mortgages and Line of Credit Facility [Line Items]
Principal amount		175.0
RTC - West | Mortgages Payable
Mortgages and Line of Credit Facility [Line Items]
Increase in principal balance		$ 20.2
The Bartlett,1221 Van Street and 220 20th Street
Mortgages and Line of Credit Facility [Line Items]
Number of mortgage loans | loan	3
Principal amount	$ 385.0