Condensed Consolidated Statements Of Operations - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	May 31, 2016	May 31, 2015	May 31, 2016	May 31, 2015
Condensed Consolidated Statements Of Operations [Abstract]
Operating revenues	$ 141,319	$ 160,707	$ 383,514	$ 436,641
Cost of operating revenues	99,511	114,321	274,847	313,785
Gross profit	41,808	46,386	108,667	122,856
Operating expenses:
Selling expense	10,606	10,682	30,961	30,330
General and administrative expense	11,882	10,719	43,925	35,270
Engineering and research expense	3,995	3,497	11,402	9,330
Total operating expenses	26,483	24,898	86,288	74,930
Operating income	15,325	21,488	22,379	47,926
Other income (expense):
Interest expense	(1,179)	(1,144)	(3,576)	(1,424)
Interest income	127	134	520	468
Other expense, net	(208)	(55)	(1,055)	(748)
Earnings before income taxes	14,065	20,423	18,268	46,222
Income tax expense	4,421	7,496	5,809	16,732
Net earnings	$ 9,644	$ 12,927	$ 12,459	$ 29,490
Earnings per share:
Basic	$ 0.90	$ 1.11	$ 1.13	$ 2.46
Diluted	$ 0.90	$ 1.10	$ 1.13	$ 2.46
Shares used in computing earnings per share:
Basic	10,709	11,690	10,997	11,965
Diluted	10,732	11,720	11,019	12,000
Cash dividends declared per share	$ 0.28	$ 0.27	$ 0.84	$ 0.81