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Other Long-Term Liabilities
6 Months Ended
Jun. 30, 2021
Other Liabilities Disclosure [Abstract]  
Other Long-Term Liabilities Other Long-Term Liabilities
Other long-term liabilities are summarized as follows (in thousands):
 June 30, 2021December 31, 2020
Black lung obligations$34,147 $34,567 
Other3,031 2,258 
Total other long-term liabilities$37,178 $36,825