NOTES PAYABLE - Schedule of Long-term Debt Instruments (Details) - USD ($) $ in Thousands	6 Months Ended
Jun. 30, 2020	Dec. 31, 2019
Debt Instrument [Line Items]
Total notes payable principal outstanding	$ 240,520	$ 417,207
Deferred financing costs, net	0	(600)
Total notes payable, net	240,520	416,607
Portfolio Loan Facility \| Secured Debt
Debt Instrument [Line Items]
Total notes payable principal outstanding	145,200
Remaining borrowing capacity	$ 48,400
Extension period	1 year
Granite Tower Mortgage Loan
Debt Instrument [Line Items]
Total notes payable principal outstanding	$ 95,400
Remaining borrowing capacity	$ 49,600
Amortization schedule of mortgage loans	30 years
Mortgage \| Corporate Technology Centre Mortgage Loan
Debt Instrument [Line Items]
Total notes payable principal outstanding	$ 0	40,564
Mortgage \| Portfolio Loan Facility
Debt Instrument [Line Items]
Total notes payable principal outstanding	$ 145,170	281,293
Effective Interest Rate	1.60%
Mortgage \| Portfolio Loan Facility \| One-month LIBOR
Debt Instrument [Line Items]
Basis spread on variable rate	1.45%
Mortgage \| Granite Tower Mortgage Loan
Debt Instrument [Line Items]
Total notes payable principal outstanding	$ 95,350	$ 95,350
Effective Interest Rate	1.80%
Mortgage \| Granite Tower Mortgage Loan \| One-month LIBOR
Debt Instrument [Line Items]
Basis spread on variable rate	1.65%

Amortization Schedule of Mortgage Loans on Real Estate

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Amount, before unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but is not limited to, notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt.

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Amount, after accumulated amortization, of debt issuance costs. Includes, but is not limited to, legal, accounting, underwriting, printing, and registration costs.

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