Industry Segment Information (Schedule Of Segment Reporting Information, By Segment) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Aug. 31, 2018	May 31, 2018	Feb. 28, 2018	Nov. 30, 2017	Aug. 31, 2017	May 31, 2017	Feb. 28, 2017	Nov. 30, 2016	Aug. 31, 2018	Aug. 31, 2017	Aug. 31, 2016
Segment Reporting Information [Line Items]
Total operating revenues	$ 123,269	$ 169,571	$ 130,339	$ 124,526	$ 131,937	$ 151,533	$ 124,125	$ 110,390	$ 547,705	$ 517,985	$ 516,411
Total operating income									38,563	40,201	34,375
Earnings before income taxes									33,853	35,715	29,288
Capital expenditures									11,054	8,863	11,496
Depreciation and amortization									16,514	16,678	16,881
Total Assets	500,256				506,032				500,256	506,032	487,515
Irrigation [Member]
Segment Reporting Information [Line Items]
Capital expenditures									9,259	6,313	8,375
Depreciation and amortization									11,412	11,840	11,774
Total Assets	277,712				337,446				277,712	337,446	332,294
Infrastructure [Member]
Segment Reporting Information [Line Items]
Capital expenditures									938	1,562	2,977
Depreciation and amortization									4,611	4,452	4,648
Total Assets	69,919				80,187				69,919	80,187	81,160
Corporate Segment
Segment Reporting Information [Line Items]
Total operating income									(27,227)	(22,704)	(33,392)
Capital expenditures									857	988	144
Depreciation and amortization									491	386	459
Total Assets	$ 152,625				$ 88,399				152,625	88,399	74,061
Operating Segments [Member]
Segment Reporting Information [Line Items]
Total operating revenues									547,705	517,985	516,411
Operating Segments [Member] | Irrigation [Member]
Segment Reporting Information [Line Items]
Total operating revenues									439,858	418,041	421,641
Total operating income									41,933	42,774	49,232
Operating Segments [Member] | Infrastructure [Member]
Segment Reporting Information [Line Items]
Total operating revenues									107,847	99,944	94,770
Total operating income									23,857	20,131	18,535
Segment Reconciling Items [Member]
Segment Reporting Information [Line Items]
Interest and other income (expense), net									(4,710)	(4,486)	(5,087)
Earnings before income taxes									$ 33,853	$ 35,715	$ 29,288