Note 20 - Concentration of Credit Risk and Major Customers - Concentration of Credit Risk (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Total Trade Receivables	$ 108,696	$ 122,715
Less: Allowance for credit losses	4,597	4,426
Total Trade Receivables, net	104,099	118,289
Accounts Receivable [Member] | Customer Concentration Risk [Member] | Thermal Coal Utilities [Member]
Total Trade Receivables	41,582	32,343
Accounts Receivable [Member] | Customer Concentration Risk [Member] | Coal Exporters and Distributors [Member]
Total Trade Receivables	53,949	82,948
Accounts Receivable [Member] | Customer Concentration Risk [Member] | Steel and Coke Producers [Member]
Total Trade Receivables	11,560	5,302
Accounts Receivable [Member] | Customer Concentration Risk [Member] | Other Customer [Member]
Total Trade Receivables	$ 1,605	$ 2,122