Industry Segment Information (Schedule of Segment Reporting Information, by Segment) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Aug. 31, 2020	May 31, 2020	Feb. 29, 2020	Nov. 30, 2019	Aug. 31, 2019	May 31, 2019	Feb. 28, 2019	Nov. 30, 2018	Aug. 31, 2020	Aug. 31, 2019	Aug. 31, 2018
Segment Reporting Information [Line Items]
Total operating revenues	$ 128,405	$ 123,106	$ 113,788	$ 109,393	$ 101,885	$ 121,054	$ 109,182	$ 111,951	$ 474,692	$ 444,072	$ 547,705
Total operating income									54,202	6,115	39,012
Other income (expense)									(5,359)	(4,008)	(5,159)
Earnings before income taxes									48,843	2,107	33,853
Capital expenditures									21,445	23,211	11,054
Depreciation and amortization									19,396	14,018	16,514
Total Assets	570,526				500,314				570,526	500,314	499,815
Irrigation [Member]
Segment Reporting Information [Line Items]
Total operating revenues									343,529	351,498	439,858
Total operating income									40,214	29,804	41,933
Capital expenditures									9,254	9,473	9,259
Depreciation and amortization									12,906	9,500	11,412
Total Assets	307,537				292,202				307,537	292,202	277,712
Irrigation [Member] | North America [Member]
Segment Reporting Information [Line Items]
Total operating revenues									218,954	218,627	294,617
Irrigation [Member] | International [Member]
Segment Reporting Information [Line Items]
Total operating revenues									124,575	132,871	145,241
Infrastructure [Member]
Segment Reporting Information [Line Items]
Total operating revenues									131,163	92,574	107,847
Total operating income									43,771	16,599	23,857
Capital expenditures									11,275	4,928	938
Depreciation and amortization									3,495	3,663	4,611
Total Assets	113,111				85,848				113,111	85,848	69,919
Corporate Segment
Segment Reporting Information [Line Items]
Total operating income									(29,783)	(40,288)	(26,778)
Capital expenditures									916	8,810	857
Depreciation and amortization									2,994	855	491
Total Assets	$ 149,878				$ 122,264				$ 149,878	$ 122,264	$ 152,184