Note 5 - Disaggregation of Revenue - Schedule of Disaggregation of Revenue (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Revenue	$ 1,062,129	$ 1,065,189	$ 2,696,214	$ 2,616,887
Water and Mineral Services [Member]
Revenue	136,275	109,428	369,357	318,398
Transportation [Member]
Revenue	568,186	623,999	1,444,450	1,510,001
Transportation [Member] | Water and Mineral Services [Member]
Revenue	0	0	0	0
Water [Member]
Revenue	121,968	106,599	335,153	317,980
Water [Member] | Water and Mineral Services [Member]
Revenue	103,505	85,331	282,076	259,690
Specialty [Member]
Revenue	234,300	205,134	590,245	513,087
Specialty [Member] | Water and Mineral Services [Member]
Revenue	27,527	19,215	73,954	48,098
Materials [Member]
Revenue	137,675	129,457	326,366	275,819
Materials [Member] | Water and Mineral Services [Member]
Revenue	5,243	4,882	13,327	10,610
California 1[Member]
Revenue	332,070	373,658	848,307	822,288
California 1[Member] | Transportation [Member]
Revenue	191,146	224,636	478,823	478,590
California 1[Member] | Water [Member]
Revenue	8,531	10,498	27,512	24,225
California 1[Member] | Specialty [Member]
Revenue	56,364	62,623	153,497	158,076
California 1[Member] | Materials [Member]
Revenue	76,029	75,901	188,475	161,397
Federal [Member]
Revenue	33,798	32,246	80,039	85,375
Federal [Member] | Transportation [Member]
Revenue	4,442	3,140	9,593	5,306
Federal [Member] | Water [Member]
Revenue	9	341	166	1,309
Federal [Member] | Specialty [Member]
Revenue	29,347	28,765	70,280	78,760
Federal [Member] | Materials [Member]
Revenue	0	0	0	0
Heavy Civil [Member]
Revenue	180,424	188,311	549,660	576,186
Heavy Civil [Member] | Transportation [Member]
Revenue	138,201	165,434	445,812	519,963
Heavy Civil [Member] | Water [Member]
Revenue	7,799	9,985	21,197	28,260
Heavy Civil [Member] | Specialty [Member]
Revenue	34,424	12,892	82,651	27,963
Heavy Civil [Member] | Materials [Member]
Revenue	0	0	0	0
Midwest [Member]
Revenue	60,375	68,288	155,321	177,776
Midwest [Member] | Transportation [Member]
Revenue	34,767	43,896	83,945	103,081
Midwest [Member] | Water [Member]
Revenue	0	0	0	152
Midwest [Member] | Specialty [Member]
Revenue	25,608	24,392	71,376	74,543
Midwest [Member] | Materials [Member]
Revenue	0	0	0	0
Northwest [Member]
Revenue	319,187	293,258	693,530	636,864
Northwest [Member] | Transportation [Member]
Revenue	199,630	186,893	426,277	403,061
Northwest [Member] | Water [Member]
Revenue	2,124	444	4,202	4,344
Northwest [Member] | Specialty [Member]
Revenue	61,030	57,247	138,487	125,647
Northwest [Member] | Materials [Member]
Revenue	$ 56,403	$ 48,674	$ 124,564	$ 103,812