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COMMITMENTS AND CONTINGENCIES Narrative 3 - Lessor Revenues (Details)
$ in Millions
12 Months Ended
Dec. 31, 2017
USD ($)
Commitments and Contingencies Disclosure [Abstract]  
Lessor leasing arrangements, operating leases, term of contract 10 years
Lessor leasing arrangements, operating leases, renewal term 10 years
Operating lease revenues $ 39.1
Future minimum revenue (lessor) $ 352.2
Lessor leasing arrangements, operating leases, remaining term of contract 9 years
Leased storage assets, cost $ 229.8
Leased storage assets, accumulated depreciation $ 104.9