Note 17 - Segment Information - Segment Revenue (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Revenue	$ 303,222	$ 121,296	$ 633,982	$ 396,396
Revenue Benchmark [Member] | Pennsylvania Mining Complex [Member] | Customer Concentration Risk [Member] | Customer A [Member]
Revenue	32,236		89,916	48,829
Revenue Benchmark [Member] | Pennsylvania Mining Complex [Member] | Customer Concentration Risk [Member] | Customer B [Member]
Revenue	38,957	30,032	72,196	134,386
Revenue Benchmark [Member] | Pennsylvania Mining Complex [Member] | Customer Concentration Risk [Member] | Customer C [Member]
Revenue	34,439	$ 14,060	71,038	$ 49,743
Revenue Benchmark [Member] | Pennsylvania Mining Complex [Member] | Customer Concentration Risk [Member] | Customer D [Member]
Revenue	37,121		$ 81,357
Revenue Benchmark [Member] | Pennsylvania Mining Complex [Member] | Customer Concentration Risk [Member] | Customer E [Member]
Revenue	$ 30,439