INCOME TAXES - Deferred Tax Assets (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017	Dec. 31, 2016
Non-current Deferred Tax Asset (Liability)
Accumulated net operating losses of TRS	$ 194	$ 337
Unrealized gain	218	251
Capitalized transaction costs	117	122
Deferred income	80	57
AMT Credit	0	19	$ 12
Deferred tax asset (liability)	609	786
Valuation allowance	(609)	(767)
Net non-current deferred tax asset (liability)	$ 0	$ 19