ACCRUED AND OTHER LIABILITIES - Reserve for Tenant Improvements and Environmental Reserves (Details)			3 Months Ended				12 Months Ended		60 Months Ended
	Jun. 30, 2016 USD ($)	Dec. 31, 2015 USD ($) a	Mar. 31, 2020 USD ($)	Mar. 31, 2019 USD ($)	Dec. 31, 2017 USD ($)	Jun. 30, 2016 USD ($)	Dec. 31, 2015 USD ($) a	Dec. 31, 2014 USD ($) a	Dec. 31, 2018 USD ($)	Feb. 21, 2020 USD ($)	Jan. 24, 2020 USD ($) tenant
Environmental Reserve for Monitoring Environmental Remediation Work Previously Performed
Environmental reserves
Additional environmental reserve accrued					$ 51,000		$ 500,000	$ 110,000	$ 661,000
Environmental costs funded			$ 580,000
Environmental reserve accrued			81,000
Wetlands restoration
Environmental reserves
Area of land (in acres) | a		148.4					148.4
Estimated cost	$ 2,000,000		2,400,000	$ 2,400,000		$ 2,000,000
Environmental costs funded			2,300,000
Accrued restoration cost		$ 1,700,000	87,000				$ 1,700,000
Increase in accrual of remediation costs				$ 361,000		$ 300,000
Minimum | Environmental Reserve for Monitoring Environmental Remediation Work Previously Performed
Environmental reserves
Estimated cost							500,000
Minimum | Wetlands restoration
Environmental reserves
Estimated cost		1,700,000
Maximum | Environmental Reserve for Monitoring Environmental Remediation Work Previously Performed
Environmental reserves
Area of land (in acres) | a								1
Estimated cost							$ 1,000,000
Maximum | Wetlands restoration
Environmental reserves
Estimated cost		$ 1,900,000
Atlanta, Georgia
Environmental reserves
Tenant improvement allowances and leasing commissions										$ 460,000
Payment of tenant improvement allowances and leasing commissions			0
Chandler, Arizona
Environmental reserves
Tenant improvement allowances and leasing commissions											$ 1,300,000
Payment of tenant improvement allowances and leasing commissions			$ 0
Number of tenant | tenant											2