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Other Long-Term Liabilities (Tables)
 6 Months Ended
Jun. 30, 2020
Other Liabilities Disclosure [Abstract]  
Other Long-Term Liabilities
Other long-term liabilities are summarized as follows (in thousands):
 June 30, 2020December 31, 2019
Black lung obligations$29,910  $30,233  
Other1,911  1,197  
Total other long-term liabilities$31,821  $31,430