SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Leveraged Leases (Narrative) (Details) - leveraged_lease	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Leveraged Lease [Line Items]
Number of leveraged leases	4	4
Maximum
Leveraged Lease [Line Items]
Original term (up to)	45 years	45 years