Note 6 - Disaggregation of Revenue - Schedule of Disaggregation of Revenue (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Revenue	$ 635,927	$ 581,813
Water and Mineral Services [Member]
Revenue	105,065	120,832
Transportation [Member]
Revenue	350,901	301,964
Transportation [Member] | Water and Mineral Services [Member]
Revenue	0	0
Water [Member]
Revenue	101,657	99,082
Water [Member] | Water and Mineral Services [Member]
Revenue	87,005	91,532
Specialty [Member]
Revenue	133,039	139,124
Specialty [Member] | Water and Mineral Services [Member]
Revenue	15,450	25,254
Materials [Member]
Revenue	50,330	41,643
Materials [Member] | Water and Mineral Services [Member]
Revenue	2,610	4,046
California 1[Member]
Revenue	178,199	126,099
California 1[Member] | Transportation [Member]
Revenue	94,932	69,513
California 1[Member] | Water [Member]
Revenue	5,512	1,366
California 1[Member] | Specialty [Member]
Revenue	44,488	32,155
California 1[Member] | Materials [Member]
Revenue	33,267	23,065
Federal [Member]
Revenue	27,270	15,737
Federal [Member] | Transportation [Member]
Revenue	398	27
Federal [Member] | Water [Member]
Revenue	381	508
Federal [Member] | Specialty [Member]
Revenue	26,491	15,202
Federal [Member] | Materials [Member]
Revenue	0	0
Heavy Civil [Member]
Revenue	178,022	164,103
Heavy Civil [Member] | Transportation [Member]
Revenue	167,426	159,742
Heavy Civil [Member] | Water [Member]
Revenue	7,102	4,361
Heavy Civil [Member] | Specialty [Member]
Revenue	3,494	0
Heavy Civil [Member] | Materials [Member]
Revenue	0	0
Midwest [Member]
Revenue	35,746	52,466
Midwest [Member] | Transportation [Member]
Revenue	24,243	18,061
Midwest [Member] | Water [Member]
Revenue	0	84
Midwest [Member] | Specialty [Member]
Revenue	11,503	34,321
Midwest [Member] | Materials [Member]
Revenue	0	0
Northwest [Member]
Revenue	111,625	102,576
Northwest [Member] | Transportation [Member]
Revenue	63,902	54,621
Northwest [Member] | Water [Member]
Revenue	1,657	1,231
Northwest [Member] | Specialty [Member]
Revenue	31,613	32,192
Northwest [Member] | Materials [Member]
Revenue	$ 14,453	$ 14,532