Industry Segment Information (Schedule Of Segment Reporting Information By Segment) (Details) $ in Thousands		3 Months Ended				9 Months Ended		12 Months Ended
		May 31, 2016 USD ($)	Feb. 29, 2016 USD ($)	May 31, 2015 USD ($)	Nov. 30, 2014 USD ($)	May 31, 2016 USD ($) segment	May 31, 2015 USD ($)	Aug. 31, 2012 USD ($)
Segment Reporting Information [Line Items]
Number of reportable segments | segment						2
Total operating revenues		$ 141,319		$ 160,707		$ 383,514	$ 436,641
Segment operating income		15,325		21,488		22,379	47,926
Unallocated general and administrative expenses		(11,882)		(10,719)		(43,925)	(35,270)
Earnings before income taxes		14,065		20,423		18,268	46,222
Capital expenditures		2,681		4,652		10,073	11,228
Depreciation and amortization		4,235		4,131		12,771	12,148
Environmental remediation expenses			$ 13,000		$ 1,500			$ 7,200
Operating Segments [Member]
Segment Reporting Information [Line Items]
Segment operating income		21,214		26,358		49,601	63,987
Segment Reconciling Items [Member]
Segment Reporting Information [Line Items]
Unallocated general and administrative expenses	[1]	(5,889)		(4,870)		(27,222)	(16,061)
Interest and other expense, net		(1,260)		(1,065)		(4,111)	(1,704)
Environmental remediation expenses		$ 0		$ 0		$ 13,000	$ 1,500
Total Revenue [Member]
Segment Reporting Information [Line Items]
Concentration risk, percentage		10.00%		10.00%		10.00%	10.00%
Irrigation [Member]
Segment Reporting Information [Line Items]
Number of operating segments | segment						5
Total operating revenues		$ 117,325		$ 131,289		$ 321,733	$ 354,336
Segment operating income		16,560		19,860		40,333	47,771
Capital expenditures		2,157		4,102		7,363	9,567
Depreciation and amortization		3,077		2,925		$ 9,235	8,450
Infrastructure [Member]
Segment Reporting Information [Line Items]
Number of operating segments | segment						1
Total operating revenues		23,994		29,418		$ 61,781	82,305
Segment operating income		4,654		6,498		9,268	16,216
Capital expenditures		524		550		2,710	1,661
Depreciation and amortization		$ 1,158		$ 1,206		$ 3,536	$ 3,698

[1] Includes environmental remediation expenses of $13.0 million and $1.5 million for the nine months ended May 31, 2016 and May 31, 2015, respectively. There were no environmental remediation expenses for the three months ended May 31, 2016 and May 31, 2015, respectively.