Quarterly report pursuant to Section 13 or 15(d)

Financial Instruments - Fair Value (Details)

v3.19.1
Financial Instruments - Fair Value (Details) - Derivatives designated as hedging instrument - USD ($)
$ in Thousands
Mar. 31, 2019
Dec. 31, 2018
Derivative assets:    
Total derivative assets $ 27,994 $ 20,768
Derivative liabilities:    
Total derivative liabilities 2,892 2,026
Cash Flow Hedging    
Derivative assets:    
Total derivative assets 598 1,925
Cash Flow Hedging | Prepaid and other current assets | Natural gas swaps    
Derivative assets:    
Total derivative assets 88 21
Cash Flow Hedging | Prepaid and other current assets | Interest rate caps    
Derivative assets:    
Total derivative assets 442 1,358
Cash Flow Hedging | Other long-term assets | Interest rate caps    
Derivative assets:    
Total derivative assets 68 546
Cash Flow Hedging | Accrued liabilities | Natural gas swaps    
Derivative liabilities:    
Total derivative liabilities 0 36
Cash Flow Hedging | Other long-term liabilities | Natural gas swaps    
Derivative liabilities:    
Total derivative liabilities 72 148
Cash Flow Hedging | Other long-term liabilities | Interest rate caps    
Derivative liabilities:    
Total derivative liabilities 2,820 1,842
Net Investment Hedging    
Derivative assets:    
Total derivative assets 27,396 18,843
Net Investment Hedging | Prepaid and other current assets | Cross currency swaps    
Derivative assets:    
Total derivative assets 7,224 5,499
Net Investment Hedging | Other long-term assets | Cross currency swaps    
Derivative assets:    
Total derivative assets $ 20,172 $ 13,344