SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Additional Information (Details) $ in Millions	12 Months Ended
	Dec. 31, 2017 CAD CAD / railcar	Dec. 31, 2016 USD ($)
Property, Plant and Equipment [Line Items]
Average incentive payment amount per railcar shipped (in dollars per railcar) | CAD / railcar	100
Maximum payment for railcar shipped | CAD	CAD 12,500,000.0
ARO liability | $		$ 1.0
Minimum
Property, Plant and Equipment [Line Items]
Property and equipment, useful life (in years)	5 years
Maximum
Property, Plant and Equipment [Line Items]
Property and equipment, useful life (in years)	30 years