Related Parties - Additional Information (Details) - USD ($)		3 Months Ended		6 Months Ended		12 Months Ended
	Mar. 27, 2020	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019
Related Party Transaction [Line Items]
Fee and other income		$ 7,129,000	$ 7,299,000	$ 15,690,000	$ 16,347,000
Accounts and other receivables, net		18,738,000		18,738,000		$ 19,231,000
Property management, asset management, leasing and other related services fee income		6,209,000	4,213,000	12,539,000	10,212,000
Transaction related costs		258,000	182,000	461,000	918,000
Accounts payable and accrued expenses		$ 105,924,000		105,924,000		117,356,000
Due from Affiliates					181,000,000
Repayment of note receivables				$ 36,918,000	11,000,000
Fund X [Member]
Related Party Transaction [Line Items]
Due from Affiliates						36,918,000
Repayment of note receivables	$ 36,918,000
Repayment of accrued interest	$ 349,000
Note receivables basis spread on variable rate		2.20%		2.20%
712 Fifth Avenue [Member]
Related Party Transaction [Line Items]
Equity method paramount ownership percentage		50.00%		50.00%
CNBB-RDF Holdings Otto Family [Member] | Management Agreements [Member]
Related Party Transaction [Line Items]
Fee and other income		$ 259,000	211,000	$ 707,000	420,000
Accounts and other receivables, net		0		0		0
Unconsolidated Joint Ventures and Real Estate Funds [Member] | Management Agreements [Member]
Related Party Transaction [Line Items]
Accounts and other receivables, net		3,418,000		3,418,000		2,734,000
Property management, asset management, leasing and other related services fee income		$ 5,396,000	3,511,000	$ 10,709,000	8,058,000
Hamburg Trust Consulting GMBH ("HTC") [Member]
Related Party Transaction [Line Items]
Mark-up cost percentage		10.00%		10.00%
Transaction related costs		$ 126,000	62,000	$ 265,000	686,000
Accounts payable and accrued expenses		$ 252,000		$ 252,000		$ 38,000
Hamburg Trust Consulting GMBH ("HTC") [Member] | Chairman, Chief Executive Officer and President [Member]
Related Party Transaction [Line Items]
Percentage of ownership		100.00%		100.00%
Mannheim Trust [Member] | Board of Director [Member] | 712 Fifth Avenue [Member]
Related Party Transaction [Line Items]
Equity method paramount ownership percentage		50.00%		50.00%
Lease rental income		$ 90,000	90,000	$ 181,000	181,000
Kramer Design Services [Member]
Related Party Transaction [Line Items]
Accounts payable and accrued expenses		47,000		47,000
Development expenses		$ 140,000		$ 140,000
Kramer Design Services [Member] | 712 Fifth Avenue [Member]
Related Party Transaction [Line Items]
Equity method paramount ownership percentage		50.00%		50.00%
Expense recognized		$ 14,000	$ 103,000	$ 29,000	$ 103,000