INVESTMENT IN UNCONSOLIDATED REAL ESTATE VENTURES - Summary of Financial Position of Real Estate Ventures (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Schedule of Equity Method Investments [Line Items]
Net property	$ 834,367	$ 835,983
Other assets	342,002	159,499
Other liabilities	290,071	85,681
Debt, net	585,068	365,707
Equity	301,230	544,094
Right of use asset - operating leases, net	21,656	0	$ 0
Lease Liability - operating leases	22,554	0
MAP Venture
Schedule of Equity Method Investments [Line Items]
Net property	192,582	198,043
Other assets	256,453	65,465
Other liabilities	266,200	59,348
Debt, net	181,525	180,555
Equity	1,310	23,605
Right of use asset - operating leases, net	197,100
Lease Liability - operating leases	206,400
Brandywine-AI Ventures LLC
Schedule of Equity Method Investments [Line Items]
Net property	24,651	47,043
Other assets	3,000	11,206
Other liabilities	824	2,002
Debt, net	0	26,020
Equity	26,827	30,227
Other
Schedule of Equity Method Investments [Line Items]
Net property	617,134	590,897
Other assets	82,549	82,828
Other liabilities	23,047	24,331
Debt, net	403,543	159,132
Equity	$ 273,093	$ 490,262