Note 4 - Disaggregation of Revenue - Schedule of Disaggregation of Revenue (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Revenue	$ 3,562,459	$ 3,445,606	$ 3,287,031
Water and Mineral Services [Member]
Revenue	433,580	530,729	340,504
Transportation [Member]
Revenue	2,017,989	1,892,149	1,946,750
Transportation [Member] | Water and Mineral Services [Member]
Revenue	0	0	0
Water [Member]
Revenue	440,317	468,730	345,861
Water [Member] | Water and Mineral Services [Member]
Revenue	348,984	423,336	265,704
Specialty [Member]
Revenue	723,391	727,537	625,666
Specialty [Member] | Water and Mineral Services [Member]
Revenue	68,619	89,289	58,643
Materials [Member]
Revenue	380,762	357,190	368,754
Materials [Member] | Water and Mineral Services [Member]
Revenue	15,977	18,104	16,157
California 1[Member]
Revenue	1,178,849	992,100	1,017,638
California 1[Member] | Transportation [Member]
Revenue	681,955	581,074	607,737
California 1[Member] | Water [Member]
Revenue	44,068	25,005	52,757
California 1[Member] | Specialty [Member]
Revenue	230,805	187,556	143,471
California 1[Member] | Materials [Member]
Revenue	222,021	198,465	213,673
Federal [Member]
Revenue	117,180	85,703	44,270
Federal [Member] | Transportation [Member]
Revenue	6,579	688	683
Federal [Member] | Water [Member]
Revenue	1,774	1,171	2,116
Federal [Member] | Specialty [Member]
Revenue	108,827	83,844	41,471
Federal [Member] | Materials [Member]
Revenue	0	0	0
Heavy Civil [Member]
Revenue	756,488	687,344	808,194
Heavy Civil [Member] | Transportation [Member]
Revenue	671,013	671,923	788,722
Heavy Civil [Member] | Water [Member]
Revenue	40,260	13,215	19,472
Heavy Civil [Member] | Specialty [Member]
Revenue	45,215	2,206	0
Heavy Civil [Member] | Materials [Member]
Revenue	0	0	0
Midwest [Member]
Revenue	241,190	253,822	309,018
Midwest [Member] | Transportation [Member]
Revenue	140,433	100,235	84,523
Midwest [Member] | Water [Member]
Revenue	156	39	1,930
Midwest [Member] | Specialty [Member]
Revenue	100,601	153,548	222,565
Midwest [Member] | Materials [Member]
Revenue	0	0	0
Northwest [Member]
Revenue	835,172	895,908	767,407
Northwest [Member] | Transportation [Member]
Revenue	518,009	538,229	465,085
Northwest [Member] | Water [Member]
Revenue	5,075	5,964	3,882
Northwest [Member] | Specialty [Member]
Revenue	169,324	211,094	159,516
Northwest [Member] | Materials [Member]
Revenue	$ 142,764	$ 140,621	$ 138,924