BASIS OF PRESENTATION AND SIGNIFICANT ACCOUNTING POLICIES - Revenue Recognition (Details) - USD ($) $ in Thousands	2 Months Ended	3 Months Ended										8 Months Ended	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Oct. 31, 2018	Jul. 31, 2018	Apr. 30, 2018	Jan. 31, 2018	Oct. 31, 2017	Jul. 31, 2017	Dec. 31, 2018	Dec. 31, 2019	Apr. 30, 2018	Apr. 30, 2017	May 01, 2018
Disaggregation of Revenue [Line Items]
Retained earnings	$ (390,196)	$ (390,196)						$ (395,669)				$ (429,048)	$ (390,196)	$ (395,669)
Mortgage loans receivable	16,140	16,140						10,329				10,410	16,140	10,329
Fixed lease income - operating leases												114,047	176,706
Variable lease income - operating leases												3,528	5,586
Total revenue	$ 30,287	$ 45,777	$ 47,436	$ 46,934	$ 45,608	$ 45,638	$ 45,946	$ 44,185	$ 42,716	$ 41,866	$ 40,978	121,871	185,755	$ 169,745	$ 160,104
Non-lease components
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers												0	0
Other property revenue
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers												$ 4,296	$ 3,463
Difference between Revenue Guidance in Effect before and after Topic 606 | Accounting Standards Update 2014-09
Disaggregation of Revenue [Line Items]
Retained earnings																$ 627
Mortgage loans receivable																$ 627