Note 5 - Disaggregation of Revenue - Schedule of Disaggregation of Revenue (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Revenue	$ 964,172	$ 915,771	$ 1,634,085	$ 1,551,698
Water and Mineral Services [Member]
Revenue	129,501	103,905	233,082	208,970
Transportation [Member]
Revenue	525,235	535,101	876,264	886,002
Transportation [Member] | Water and Mineral Services [Member]
Revenue	0	0	0	0
Water [Member]
Revenue	113,432	109,724	213,185	211,381
Water [Member] | Water and Mineral Services [Member]
Revenue	98,723	87,354	178,571	174,359
Specialty [Member]
Revenue	200,271	174,914	355,945	307,953
Specialty [Member] | Water and Mineral Services [Member]
Revenue	26,790	13,433	46,427	28,883
Materials [Member]
Revenue	125,234	96,032	188,691	146,362
Materials [Member] | Water and Mineral Services [Member]
Revenue	3,988	3,118	8,084	5,728
California 1[Member]
Revenue	306,214	270,431	516,237	448,630
California 1[Member] | Transportation [Member]
Revenue	176,307	159,022	287,677	253,954
California 1[Member] | Water [Member]
Revenue	7,982	8,215	18,981	13,727
California 1[Member] | Specialty [Member]
Revenue	51,435	50,965	97,133	95,453
California 1[Member] | Materials [Member]
Revenue	70,490	52,229	112,446	85,496
Federal [Member]
Revenue	22,171	25,859	46,241	53,129
Federal [Member] | Transportation [Member]
Revenue	3,297	1,768	5,151	2,166
Federal [Member] | Water [Member]
Revenue	27	587	157	968
Federal [Member] | Specialty [Member]
Revenue	18,847	23,504	40,933	49,995
Federal [Member] | Materials [Member]
Revenue	0	0	0	0
Heavy Civil [Member]
Revenue	188,137	209,853	369,236	387,875
Heavy Civil [Member] | Transportation [Member]
Revenue	155,868	187,103	307,611	354,529
Heavy Civil [Member] | Water [Member]
Revenue	6,056	11,173	13,398	18,275
Heavy Civil [Member] | Specialty [Member]
Revenue	26,213	11,577	48,227	15,071
Heavy Civil [Member] | Materials [Member]
Revenue	0	0	0	0
Midwest [Member]
Revenue	57,659	73,742	94,946	109,488
Midwest [Member] | Transportation [Member]
Revenue	32,223	34,942	49,178	59,185
Midwest [Member] | Water [Member]
Revenue	0	152	0	152
Midwest [Member] | Specialty [Member]
Revenue	25,436	38,648	45,768	50,151
Midwest [Member] | Materials [Member]
Revenue	0	0	0	0
Northwest [Member]
Revenue	260,490	231,981	374,343	343,606
Northwest [Member] | Transportation [Member]
Revenue	157,540	152,266	226,647	216,168
Northwest [Member] | Water [Member]
Revenue	644	2,243	2,078	3,900
Northwest [Member] | Specialty [Member]
Revenue	51,550	36,787	77,457	68,400
Northwest [Member] | Materials [Member]
Revenue	$ 50,756	$ 40,685	$ 68,161	$ 55,138