OPERATING SEGMENT REPORTING - Capital Expenditures (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Operating Segment Reporting
Capital Expenditures	$ 79,396	$ 11,511	$ 6,165
Mexico
Operating Segment Reporting
Capital Expenditures	(3,107)	939	5,401
Canada
Operating Segment Reporting
Capital Expenditures	(1,110)	4,301
U.S.
Operating Segment Reporting
Capital Expenditures	$ 83,613	$ 6,271	$ 764