Quarterly report pursuant to Section 13 or 15(d)

RELATED PARTIES (Narrative) (Details)

v3.19.3
RELATED PARTIES (Narrative) (Details) - USD ($)
$ in Millions
9 Months Ended 12 Months Ended
Sep. 30, 2019
Dec. 31, 2017
Dec. 31, 2018
Segment Reporting Information [Line Items]      
Noncontrolling Interest, Ownership Percentage by Parent 100.00%    
Empire      
Segment Reporting Information [Line Items]      
Noncontrolling Interest, Ownership Percentage by Parent   100.00%  
Purchase of Noncontrolling Interest   $ 132.7  
Other Liabilities [Member] | Empire      
Segment Reporting Information [Line Items]      
Noncontrolling Interest Purchase, Installment Amount $ 44.2    
Hibbing [Member]      
Segment Reporting Information [Line Items]      
Ownership interest, equity method investment 23.00%   23.00%