Note 23 - Segment Information - Segment Revenue (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Total Revenue from Contracts with Customers	$ 879,462	$ 1,375,559	$ 1,472,790
Pennsylvania Mining Complex [Member] | Revenue Benchmark [Member] | Customer Concentration Risk [Member] | Customer A [Member]
Total Revenue from Contracts with Customers	134,354	242,703	283,703
Pennsylvania Mining Complex [Member] | Revenue Benchmark [Member] | Customer Concentration Risk [Member] | Customer B [Member]
Total Revenue from Contracts with Customers	173,461	446,403	274,755
Pennsylvania Mining Complex [Member] | Revenue Benchmark [Member] | Customer Concentration Risk [Member] | Customer C [Member]
Total Revenue from Contracts with Customers	$ 116,536	$ 215,099	$ 214,152