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Debt (Details) - USD ($)
$ in Thousands
6 Months Ended 12 Months Ended
Jun. 30, 2016
Dec. 31, 2015
Jun. 04, 2013
Debt Instrument [Line Items]      
Industrial revenue bonds $ 7,815 $ 7,815  
Total debt 255,299 255,093  
Long-term Debt [Member] | Senior secured notes due June 01, 2021 [Member]      
Debt Instrument [Line Items]      
Secured secured notes $ 247,484 $ 247,278  
Maturity date Jun. 01, 2021 Jun. 01, 2021  
Stated interest rate, percentage 7.50% 7.50% 7.50%
Debt discount $ 2,516 $ 2,722  
Short-term Debt [Member] | Industrial revenue bonds due 2028 [Member]      
Debt Instrument [Line Items]      
Industrial revenue bonds $ 7,815 $ 7,815  
Maturity date Apr. 01, 2028 Apr. 01, 2028  
Stated interest rate, percentage 0.61%    
Maximum [Member] | Short-term Debt [Member] | Industrial revenue bonds due 2028 [Member]      
Debt Instrument [Line Items]      
Effective interest rate, maximum 12.00% 12.00%