Quarterly report pursuant to Section 13 or 15(d)

Financial Instruments - Fair Value (Details)

v3.10.0.1
Financial Instruments - Fair Value (Details) - Derivatives designated as hedging instrument - USD ($)
$ in Thousands
Sep. 30, 2018
Dec. 31, 2017
Derivative assets:    
Total derivative assets $ 13,486 $ 1,043
Derivative liabilities:    
Total derivative liabilities 114 448
Cash Flow Hedging    
Derivative assets:    
Total derivative assets 4,687 1,043
Cash Flow Hedging | Prepaid and other current assets | Natural gas swaps    
Derivative assets:    
Total derivative assets 248 0
Cash Flow Hedging | Prepaid and other current assets | Interest rate caps    
Derivative assets:    
Total derivative assets 1,825 44
Cash Flow Hedging | Other long-term assets | Interest rate caps    
Derivative assets:    
Total derivative assets 2,614 999
Cash Flow Hedging | Accrued liabilities | Natural gas swaps    
Derivative liabilities:    
Total derivative liabilities 0 318
Cash Flow Hedging | Other long-term liabilities | Natural gas swaps    
Derivative liabilities:    
Total derivative liabilities 114 130
Net Investment Hedging    
Derivative assets:    
Total derivative assets 8,799 0
Net Investment Hedging | Prepaid and other current assets | Cross currency swaps    
Derivative assets:    
Total derivative assets 6,894 0
Net Investment Hedging | Other long-term assets | Cross currency swaps    
Derivative assets:    
Total derivative assets $ 1,905 $ 0