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
Jun. 30, 2018
Dec. 31, 2017
Derivative assets:    
Total derivative assets $ 12,010 $ 1,043
Derivative liabilities:    
Total derivative liabilities 196 448
Cash Flow Hedging    
Derivative assets:    
Total derivative assets 4,349 1,043
Cash Flow Hedging | Prepaid and other current assets | Natural gas swaps    
Derivative assets:    
Total derivative assets 2 0
Cash Flow Hedging | Prepaid and other current assets | Interest rate caps    
Derivative assets:    
Total derivative assets 1,208 44
Cash Flow Hedging | Other long-term assets | Interest rate caps    
Derivative assets:    
Total derivative assets 3,139 999
Cash Flow Hedging | Accrued liabilities | Natural gas swaps    
Derivative liabilities:    
Total derivative liabilities 25 318
Cash Flow Hedging | Other long-term liabilities | Natural gas swaps    
Derivative liabilities:    
Total derivative liabilities 171 130
Net Investment Hedging    
Derivative assets:    
Total derivative assets 7,661 0
Net Investment Hedging | Prepaid and other current assets | Cross currency swaps    
Derivative assets:    
Total derivative assets 5,367 0
Net Investment Hedging | Other long-term assets | Cross currency swaps    
Derivative assets:    
Total derivative assets $ 2,294 $ 0