Leases - Operating Leases - Additional Information (Details) $ in Thousands	3 Months Ended	6 Months Ended
	Jun. 30, 2019 USD ($) shopping_center	Jun. 30, 2019 USD ($) item shopping_center	Jun. 30, 2018 USD ($)
Operating Leased Assets [Line Items]
Variable lease revenues	$ 13,200	$ 26,600
Cumulative effect adjustment to retained earnings required upon adoption of the new standard	0	0
Operating lease, right-of-use asset	56,279	$ 56,279
Number of operating lease | item		9
Number of finance lease | item		4
Finance lease, right-of-use asset	93,796	$ 93,796
Finance lease, liability	87,784	87,784
Operating lease liabilities	$ 57,397	57,397
Acquisition of real estate		$ 138,716	$ 46,171
Number of shopping centers with land leases | shopping_center	6	6
Ground lease expense			800
Rent expense capitalized			300
Rent expense			500
Capital lease term		49 years
1238 Wisconsin Avenue
Operating Leased Assets [Line Items]
Finance lease, right-of-use asset	$ 11,200	$ 11,200
Finance lease, liability	10,700	10,700
110 University Place
Operating Leased Assets [Line Items]
Operating lease, right-of-use asset	45,300	45,300
Operating lease liabilities	45,300	45,300
Acquisition of real estate	10,500
Capital Lease Liability
Operating Leased Assets [Line Items]
Finance lease liabilities	71,100	71,100
Finance lease, liability	71,100	71,100
Repayments capital lease obligations			$ 1,300
Ground, Office and Equipment Leases
Operating Leased Assets [Line Items]
Operating lease, right-of-use asset	82,600	82,600
Operating lease liabilities	76,600	76,600
Capital Leases Asset
Operating Leased Assets [Line Items]
Finance lease, right-of-use asset	77,000	77,000
Accounting Standards Update 2016-02
Operating Leased Assets [Line Items]
Operating lease, right-of-use asset	11,900	11,900
Operating lease liabilities	12,800	12,800
Finance lease, right-of-use asset	5,700	5,700
Finance lease, liability	$ 5,700	$ 5,700
Minimum
Operating Leased Assets [Line Items]
Operating lease term	1 month	1 month
Period of lease term		25 years
Maximum
Operating Leased Assets [Line Items]
Operating lease term	60 years	60 years
Period of lease term		71 years