Note 5 - Disaggregation of Revenue - Schedule of Disaggregation of Revenue (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Revenue	$ 669,913	$ 635,927
Water and Mineral Services [Member]
Revenue	103,581	105,065
Transportation [Member]
Revenue	351,029	350,901
Transportation [Member] | Water and Mineral Services [Member]
Revenue	0	0
Water [Member]
Revenue	99,753	101,657
Water [Member] | Water and Mineral Services [Member]
Revenue	79,848	87,005
Specialty [Member]
Revenue	155,674	133,039
Specialty [Member] | Water and Mineral Services [Member]
Revenue	19,637	15,450
Materials [Member]
Revenue	63,457	50,330
Materials [Member] | Water and Mineral Services [Member]
Revenue	4,096	2,610
California 1[Member]
Revenue	210,023	178,199
California 1[Member] | Transportation [Member]
Revenue	111,370	94,932
California 1[Member] | Water [Member]
Revenue	10,999	5,512
California 1[Member] | Specialty [Member]
Revenue	45,698	44,488
California 1[Member] | Materials [Member]
Revenue	41,956	33,267
Federal [Member]
Revenue	24,070	27,270
Federal [Member] | Transportation [Member]
Revenue	1,854	398
Federal [Member] | Water [Member]
Revenue	130	381
Federal [Member] | Specialty [Member]
Revenue	22,086	26,491
Federal [Member] | Materials [Member]
Revenue	0	0
Heavy Civil [Member]
Revenue	181,099	178,022
Heavy Civil [Member] | Transportation [Member]
Revenue	151,743	167,426
Heavy Civil [Member] | Water [Member]
Revenue	7,342	7,102
Heavy Civil [Member] | Specialty [Member]
Revenue	22,014	3,494
Heavy Civil [Member] | Materials [Member]
Revenue	0	0
Midwest [Member]
Revenue	37,287	35,746
Midwest [Member] | Transportation [Member]
Revenue	16,955	24,243
Midwest [Member] | Water [Member]
Revenue	0	0
Midwest [Member] | Specialty [Member]
Revenue	20,332	11,503
Midwest [Member] | Materials [Member]
Revenue	0	0
Northwest [Member]
Revenue	113,853	111,625
Northwest [Member] | Transportation [Member]
Revenue	69,107	63,902
Northwest [Member] | Water [Member]
Revenue	1,434	1,657
Northwest [Member] | Specialty [Member]
Revenue	25,907	31,613
Northwest [Member] | Materials [Member]
Revenue	$ 17,405	$ 14,453