Note 16 - Segment Information - Segment Revenue (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Revenue	$ 330,760	$ 275,100
Pennsylvania Mining Complex [Member] | Revenue Benchmark [Member] | Customer Concentration Risk [Member] | Customer A [Member]
Revenue	57,680	38,908
Pennsylvania Mining Complex [Member] | Revenue Benchmark [Member] | Customer Concentration Risk [Member] | Customer B [Member]
Revenue	33,239	104,354
Pennsylvania Mining Complex [Member] | Revenue Benchmark [Member] | Customer Concentration Risk [Member] | Customer C [Member]
Revenue	36,599	$ 35,683
Pennsylvania Mining Complex [Member] | Revenue Benchmark [Member] | Customer Concentration Risk [Member] | Customer D [Member]
Revenue	$ 44,236