Note 20 - Concentration of Credit Risk and Major Customers - Concentration of Credit Risk (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Total Trade Receivables	$ 122,715	$ 133,788
Less: Allowance for credit losses	4,426	2,100
Total Trade Receivables, net	118,289	131,688
Accounts Receivable [Member] | Customer Concentration Risk [Member] | Thermal Coal Utilities [Member]
Total Trade Receivables	32,343	58,557
Accounts Receivable [Member] | Customer Concentration Risk [Member] | Coal Exporters and Distributors [Member]
Total Trade Receivables	82,948	73,416
Accounts Receivable [Member] | Customer Concentration Risk [Member] | Steel and Coke Producers [Member]
Total Trade Receivables	5,302	0
Accounts Receivable [Member] | Customer Concentration Risk [Member] | Other Customer [Member]
Total Trade Receivables	$ 2,122	$ 1,815