Note 6 - Unearned Revenue - Schedule of Unearned Revenue (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Jun. 30, 2021	Sep. 30, 2020
Unearned Revenue	$ 3,032,192	$ 3,452,021	$ 3,114,354
Water and Mineral Services [Member]
Unearned Revenue	159,958	153,051	118,938
California 1[Member]
Unearned Revenue	845,595	963,504	731,334
Federal [Member]
Unearned Revenue	116,369	110,348	121,554
Heavy Civil [Member]
Unearned Revenue	791,621	956,941	1,309,264
Midwest [Member]
Unearned Revenue	372,899	403,077	276,232
Northwest [Member]
Unearned Revenue	745,750	865,100	557,032
Transportation [Member]
Unearned Revenue	1,803,664	2,075,498	2,311,906
Transportation [Member] | Water and Mineral Services [Member]
Unearned Revenue	0	0	0
Transportation [Member] | California 1[Member]
Unearned Revenue	695,445	769,260	562,988
Transportation [Member] | Federal [Member]
Unearned Revenue	40,477	7,303	13,787
Transportation [Member] | Heavy Civil [Member]
Unearned Revenue	513,590	622,491	1,060,034
Transportation [Member] | Midwest [Member]
Unearned Revenue	85,755	107,630	169,538
Transportation [Member] | Northwest [Member]
Unearned Revenue	468,397	568,814	505,559
Water [Member]
Unearned Revenue	353,731	362,713	197,554
Water [Member] | Water and Mineral Services [Member]
Unearned Revenue	159,958	153,051	118,938
Water [Member] | California 1[Member]
Unearned Revenue	35,972	44,066	52,598
Water [Member] | Federal [Member]
Unearned Revenue	65	73	494
Water [Member] | Heavy Civil [Member]
Unearned Revenue	154,005	161,632	24,803
Water [Member] | Midwest [Member]
Unearned Revenue	0	0	0
Water [Member] | Northwest [Member]
Unearned Revenue	3,731	3,891	721
Specialty [Member]
Unearned Revenue	874,797	1,013,810	604,894
Specialty [Member] | Water and Mineral Services [Member]
Unearned Revenue	0	0	0
Specialty [Member] | California 1[Member]
Unearned Revenue	114,178	150,178	115,748
Specialty [Member] | Federal [Member]
Unearned Revenue	75,827	102,972	107,273
Specialty [Member] | Heavy Civil [Member]
Unearned Revenue	124,026	172,818	224,427
Specialty [Member] | Midwest [Member]
Unearned Revenue	287,144	295,447	106,694
Specialty [Member] | Northwest [Member]
Unearned Revenue	$ 273,622	$ 292,395	$ 50,752