XML 106 R79.htm IDEA: XBRL DOCUMENT v3.3.1.900
Acquired Sales Contracts (Schedule of Acquired Sales Contracts) (Details) - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2015
Dec. 31, 2014
Dec. 31, 2013
Acquired Finite-Lived Intangible Assets And Liabilities By Major Class [Line Items]      
Prepaid royalties $ 41,990 $ 15,356 $ 1,104
Acquired fair value, Assets 131,299 131,299  
Acquired fair value, Liabilities 166,697 166,697  
Accumulated amortization, Asset (130,839) (130,363)  
Accumulated amortization, Liabilities (151,354) (134,988)  
Total, Assets 460 936  
Total, Liabilities 15,343 31,709  
Net total, Liabilities (14,883) (30,773)  
Coal Supply Agreement, Liabilities 3,852 12,453  
Other Current Assets [Member]      
Acquired Finite-Lived Intangible Assets And Liabilities By Major Class [Line Items]      
Coal supply agreement, Assets 460 462  
Accrued Liabilities [Member]      
Acquired Finite-Lived Intangible Assets And Liabilities By Major Class [Line Items]      
Coal Supply Agreement, Liabilities 3,852 12,453  
Other Assets [Member]      
Acquired Finite-Lived Intangible Assets And Liabilities By Major Class [Line Items]      
Coal supply agreement, Assets 0 474  
Other Noncurrent Liabilities [Member]      
Acquired Finite-Lived Intangible Assets And Liabilities By Major Class [Line Items]      
Coal Supply Agreement, Liabilities $ 11,491 $ 19,256