Note 16 - Segment Information - Segment Revenue (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Revenue	$ 214,292	$ 321,444	$ 610,688	$ 1,049,609
Pennsylvania Mining Complex [Member] | Revenue Benchmark [Member] | Customer Concentration Risk [Member] | Customer A [Member]
Revenue	45,818	49,772	94,647	180,014
Pennsylvania Mining Complex [Member] | Revenue Benchmark [Member] | Customer Concentration Risk [Member] | Customer C [Member]
Revenue	$ 36,888	63,526	86,631	158,903
Pennsylvania Mining Complex [Member] | Revenue Benchmark [Member] | Customer Concentration Risk [Member] | Customer B [Member]
Revenue		$ 95,953	$ 141,993	$ 358,882