Annual report pursuant to Section 13 and 15(d)

Fair Value Measurements - Assets and Liabilities Measured at Fair Value on a Recurring Basis (Details)

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Fair Value Measurements - Assets and Liabilities Measured at Fair Value on a Recurring Basis (Details) - USD ($)
$ in Thousands
Dec. 31, 2019
Dec. 31, 2018
Liabilities:    
Derivative contracts $ 11,182 $ 0
Recurring    
Assets:    
Derivative contracts 3,928 20,768
Restoration plan assets 4,199 4,244
Total 8,127 25,012
Liabilities:    
Derivative contracts 12,415 2,026
Recurring | Quoted Prices in Active Markets (Level 1)    
Assets:    
Derivative contracts 0 0
Restoration plan assets 4,199 4,244
Total 4,199 4,244
Liabilities:    
Derivative contracts 0 0
Recurring | Significant Other Observable Inputs (Level 2)    
Assets:    
Derivative contracts 3,928 20,768
Restoration plan assets 0 0
Total 3,928 20,768
Liabilities:    
Derivative contracts 12,415 2,026
Recurring | Significant Unobservable Inputs (Level 3)    
Assets:    
Derivative contracts 0 0
Restoration plan assets 0 0
Total 0 0
Liabilities:    
Derivative contracts $ 0 $ 0