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Debt (Details) - USD ($)
$ in Thousands
3 Months Ended 12 Months Ended
Mar. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Jun. 04, 2013
Debt Instrument [Line Items]        
Industrial revenue bonds $ 7,815 $ 7,815 $ 7,815  
Total 255,624 255,514 255,093  
Industrial revenue bonds due 2028 [Member] | Short-term Debt [Member]        
Debt Instrument [Line Items]        
Industrial revenue bonds $ 7,815 $ 7,815 $ 7,815  
Stated interest rate 1.11% 0.92%    
Maturity date Apr. 01, 2028 Apr. 01, 2028 Apr. 01, 2028  
Senior secured notes due June 01, 2021 [Member] | Long-term Debt [Member]        
Debt Instrument [Line Items]        
Senior secured notes $ 247,809 $ 247,699 $ 247,278  
Stated interest rate 7.50% 7.50% 7.50% 7.50%
Maturity date Jun. 01, 2021 Jun. 01, 2021 Jun. 01, 2021  
Debt discount $ 2,191 $ 2,301 $ 2,722  
Maximum [Member] | Industrial revenue bonds due 2028 [Member] | Short-term Debt [Member]        
Debt Instrument [Line Items]        
Effective interest rate (percent) 12.00% 12.00% 12.00%