ASSETS HELD FOR SALE ASSETS HELD FOR SALE - Schedule for assets held for sale (Details) $ in Thousands	1 Months Ended	3 Months Ended	12 Months Ended
	Dec. 31, 2016 building	Mar. 31, 2019 USD ($) segment	Dec. 31, 2018 USD ($) segment	Dec. 31, 2017 USD ($)
Long Lived Assets Held-for-sale [Line Items]
Sale price subject to prorations and adjustments		$ 24,500
Assets held for sale		21,337	$ 21,328
Assets Held-For-Sale, Not Part Of Disposal Group, Property, Plant, And Equipment, Gross		22,063
Assets Held-For-Sale, Not Part Of Disposal Group, Property, Plant, And Equipment, Accumulated Depreciation, Depletion And Amortization		(1,278)
Assets Held-For-Sale, Not Part Of Disposal Group, Property, Plant, And Equipment, Net		20,785
Assets Held-For-Sale, Not Part Of Disposal Group, Finite-Lived Intangible Assets, Gross		961
Accumulated Amortization		(52,368)	$ (38,941)
Assets Held-For-Sale, Not Part Of Disposal Group, Finite-Lived Intangible Assets, Net		$ 493
Number of reportable segments | segment		1	1
Land
Long Lived Assets Held-for-sale [Line Items]
Assets held for sale		$ 5,818
Building
Long Lived Assets Held-for-sale [Line Items]
Assets held for sale		14,984
Site improvements
Long Lived Assets Held-for-sale [Line Items]
Assets held for sale		950
Computer equipment and capitalized software
Long Lived Assets Held-for-sale [Line Items]
Assets held for sale		166
Furniture and other equipment
Long Lived Assets Held-for-sale [Line Items]
Assets held for sale		145
Tenant leases
Long Lived Assets Held-for-sale [Line Items]
Assets held for sale		961
Accumulated Amortization		$ (468)
Two Office Buildings In Charlotte, NC [Member]
Long Lived Assets Held-for-sale [Line Items]
Number Of Office Buildings Acquired | building	2
Fixed assets				$ 23,500
Acquisition Costs, Period Cost				$ 100