Note 17 - Business Segment Information - Segment Reporting Information (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2020
Total revenue	$ 964,172	$ 915,771	$ 1,634,085	$ 1,551,698
Gross profit	116,946	88,343	180,264	112,142
Depreciation, depletion and amortization	25,248	26,175	47,251	52,121
Segment assets	2,478,898	2,508,654	2,478,898	2,508,654	$ 2,379,996
Transportation [Member]
Total revenue	525,235	535,101	876,264	886,002
Gross profit	59,517	31,197	95,383	56,566
Depreciation, depletion and amortization	5,570	4,391	10,082	9,417
Water [Member]
Total revenue	113,432	109,724	213,185	211,381
Gross profit	10,563	12,579	19,129	21,926
Depreciation, depletion and amortization	7,323	9,577	14,603	19,141
Specialty [Member]
Total revenue	200,271	174,914	355,945	307,953
Gross profit	24,369	25,280	41,694	14,561
Depreciation, depletion and amortization	5,674	6,737	10,251	13,120
Materials [Member]
Total revenue	125,234	96,032	188,691	146,362
Gross profit	22,497	19,287	24,058	19,089
Depreciation, depletion and amortization	6,681	5,470	12,315	10,443
Operating Segments [Member]
Total revenue	1,015,779	961,597	1,701,384	1,611,846
Gross profit	116,946	88,343	180,264	112,142
Segment assets	891,445	1,073,487	891,445	1,073,487
Operating Segments [Member] | Transportation [Member]
Total revenue	525,235	535,101	876,264	886,002
Segment assets	308,918	304,312	308,918	304,312
Operating Segments [Member] | Water [Member]
Total revenue	113,432	109,724	213,185	211,381
Segment assets	113,986	267,385	113,986	267,385
Operating Segments [Member] | Specialty [Member]
Total revenue	200,271	174,914	355,945	307,953
Segment assets	104,128	123,881	104,128	123,881
Operating Segments [Member] | Materials [Member]
Total revenue	176,841	141,858	255,990	206,510
Segment assets	364,413	377,909	364,413	377,909
Consolidation, Eliminations [Member]
Total revenue	(51,607)	(45,826)	(67,299)	(60,148)
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	$ (51,607)	$ (45,826)	$ (67,299)	$ (60,148)