Industry Segment Information (Schedule Of Segment Reporting Information, By Segment)(Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Aug. 31, 2012	May 31, 2012	Feb. 29, 2012	Nov. 30, 2011	Aug. 31, 2011	May 31, 2011	Feb. 28, 2011	Nov. 30, 2010	Aug. 31, 2012	Aug. 31, 2011	Aug. 31, 2010
Segment Reporting Information [Line Items]
Total operating revenues	$ 127,817	$ 172,099	$ 132,134	$ 119,205	$ 116,110	$ 153,446	$ 120,168	$ 89,166	$ 551,255	$ 478,890	$ 358,440
Operating Income (Loss)									65,510	56,586	37,842
Segment operating income									80,248	71,604	51,952
Unallocated general and administrative expenses									(14,738)	(15,018)	(14,110)
Interest and other income (expense), net									(402)	(72)	(1,060)
Total	12,653	28,587	19,427	4,441	9,777	23,159	17,001	6,577	65,108	56,514	36,782
Capital Expenditures									9,890	8,405	5,784
Depreciation and Amortization									12,468	11,734	10,710
Assets	415,531				381,144				415,531	381,144	325,481
Irrigation [Member]
Segment Reporting Information [Line Items]
Operating revenues									475,299	369,930	258,666
Operating Income (Loss)									80,259	59,703	40,869
Capital Expenditures									7,942	5,490	3,125
Depreciation and Amortization									6,959	6,009	4,597
Assets	303,741				267,275				303,741	267,275	206,885
Infrastructure [Member]
Segment Reporting Information [Line Items]
Operating revenues									75,956	108,960	99,774
Operating Income (Loss)									(11)	11,901	11,083
Capital Expenditures									1,948	2,915	2,659
Depreciation and Amortization									5,509	5,725	6,113
Assets	$ 111,790				$ 113,869				$ 111,790	$ 113,869	$ 118,596