Note 6 - Unearned Revenue - Schedule of Unearned Revenue (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020	Mar. 31, 2020
Unearned Revenue	$ 3,325,737	$ 2,929,952	$ 3,600,028
Water and Mineral Services [Member]
Unearned Revenue	154,185	119,124	143,539
California 1[Member]
Unearned Revenue	809,450	798,931	674,113
Federal [Member]
Unearned Revenue	132,384	90,008	150,678
Heavy Civil [Member]
Unearned Revenue	974,847	1,144,522	1,603,014
Midwest [Member]
Unearned Revenue	485,718	228,467	349,483
Northwest [Member]
Unearned Revenue	769,153	548,900	679,201
Transportation [Member]
Unearned Revenue	2,064,848	2,169,682	2,691,091
Transportation [Member] | Water and Mineral Services [Member]
Unearned Revenue	0	0	0
Transportation [Member] | California 1[Member]
Unearned Revenue	627,002	618,429	527,971
Transportation [Member] | Federal [Member]
Unearned Revenue	10,028	11,895	18,152
Transportation [Member] | Heavy Civil [Member]
Unearned Revenue	774,123	913,430	1,321,443
Transportation [Member] | Midwest [Member]
Unearned Revenue	135,655	138,246	208,872
Transportation [Member] | Northwest [Member]
Unearned Revenue	518,040	487,682	614,653
Water [Member]
Unearned Revenue	190,253	175,134	241,161
Water [Member] | Water and Mineral Services [Member]
Unearned Revenue	154,185	119,124	143,539
Water [Member] | California 1[Member]
Unearned Revenue	27,754	38,716	52,136
Water [Member] | Federal [Member]
Unearned Revenue	100	227	957
Water [Member] | Heavy Civil [Member]
Unearned Revenue	6,791	14,605	41,511
Water [Member] | Midwest [Member]
Unearned Revenue	0	0	150
Water [Member] | Northwest [Member]
Unearned Revenue	1,423	2,462	2,868
Specialty [Member]
Unearned Revenue	1,070,636	585,136	667,776
Specialty [Member] | Water and Mineral Services [Member]
Unearned Revenue	0	0	0
Specialty [Member] | California 1[Member]
Unearned Revenue	154,694	141,786	94,006
Specialty [Member] | Federal [Member]
Unearned Revenue	122,256	77,886	131,569
Specialty [Member] | Heavy Civil [Member]
Unearned Revenue	193,933	216,487	240,060
Specialty [Member] | Midwest [Member]
Unearned Revenue	350,063	90,221	140,461
Specialty [Member] | Northwest [Member]
Unearned Revenue	$ 249,690	$ 58,756	$ 61,680