Note 17 - Business Segment Information - Segment Reporting Information (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Total revenue	$ 1,062,129	$ 1,065,189	$ 2,696,214	$ 2,616,887
Gross profit	119,935	125,997	300,199	238,139
Depreciation, depletion and amortization	25,244	24,692	72,495	76,813
Segment assets	2,561,756	2,488,273	2,561,756	2,488,273	$ 2,379,996
Transportation [Member]
Total revenue	568,186	623,999	1,444,450	1,510,001
Gross profit	58,503	54,322	153,886	110,888
Depreciation, depletion and amortization	5,513	5,268	15,595	14,685
Water [Member]
Total revenue	121,968	106,599	335,153	317,980
Gross profit	9,876	12,557	29,005	34,483
Depreciation, depletion and amortization	7,074	8,258	21,677	27,399
Specialty [Member]
Total revenue	234,300	205,134	590,245	513,087
Gross profit	30,858	33,292	72,552	47,853
Depreciation, depletion and amortization	5,643	5,046	15,894	18,166
Materials [Member]
Total revenue	137,675	129,457	326,366	275,819
Gross profit	20,698	25,826	44,756	44,915
Depreciation, depletion and amortization	7,014	6,120	19,329	16,563
Operating Segments [Member]
Total revenue	1,125,873	1,130,030	2,827,257	2,741,876
Gross profit	119,935	125,997	300,199	238,139
Segment assets	869,342	929,225	869,342	929,225
Operating Segments [Member] | Transportation [Member]
Total revenue	568,186	623,999	1,444,450	1,510,001
Segment assets	305,800	305,962	305,800	305,962
Operating Segments [Member] | Water [Member]
Total revenue	121,968	106,599	335,153	317,980
Segment assets	107,327	142,604	107,327	142,604
Operating Segments [Member] | Specialty [Member]
Total revenue	234,300	205,134	590,245	513,087
Segment assets	100,279	118,797	100,279	118,797
Operating Segments [Member] | Materials [Member]
Total revenue	201,419	194,298	457,409	400,808
Segment assets	355,936	361,862	355,936	361,862
Consolidation, Eliminations [Member]
Total revenue	(63,744)	(64,841)	(131,043)	(124,989)
Consolidation, Eliminations [Member] | Transportation [Member]
Total revenue	0	0	0	0
Consolidation, Eliminations [Member] | Water [Member]
Total revenue	0	0	0	0
Consolidation, Eliminations [Member] | Specialty [Member]
Total revenue	0	0	0	0
Consolidation, Eliminations [Member] | Materials [Member]
Total revenue	$ (63,744)	$ (64,841)	$ (131,043)	$ (124,989)