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LONG-TERM DEBT, LETTERS OF CREDIT AND DERIVATIVES - Convertible Debt Narrative (Details)
9 Months Ended
Sep. 30, 2020
shares
numberOfDay
$ / shares
Jul. 31, 2017
USD ($)
Debt Instrument [Line Items]    
Debt instrument, convertible, threshold percentage of stock price trigger for redemption 130.00%  
Debt instrument, convertible, threshold trading days for redemption | numberOfDay 20  
Threshold consecutive trading days for redemption 30 days  
Percentage of the maximum number of shares authorized for issuance 40.00%  
Percentage of maximum number of shares that would require cash settlement 60.00%  
Remaining amortization period of convertible debt 34 months  
Convertible debt    
Debt Instrument [Line Items]    
Principal amount, long-term debt issued | $   $ 230,000,000.0
Interest rate on convertible debt 5.00% 5.00%
Initial conversion rate, convertible debt 46.0829  
Initial conversion price, convertible debt (in dollars per share) | $ / shares $ 21.70  
Threshold trading days | numberOfDay 20  
Threshold consecutive trading days | numberOfDay 30  
Threshold percentage of stock price trigger 130.00%  
Number of business days after the specified trading price criteria met that notes may be converted | numberOfDay 5  
Consecutive trading days, trading price criteria 5 days  
Convertible debt, threshold percentage, product of common stock price and conversion price 98.00%  
Number of shares into which debt is convertible (in shares) | shares 10,599,067  
Shares outstanding, percentage threshold (more than) 19.99%  
Convertible debt, threshold shares, approval of shareholders | shares 5,964,858  
Redemption price, percentage (equal to) 100.00%  
Convertible debt | Maximum    
Debt Instrument [Line Items]    
Number of shares into which debt is convertible (in shares) | shares 14,838,703  
Number of shares that would require cash settlement | shares 8,873,845