Condensed Consolidated Statements Of Operations - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	May. 31, 2015	May. 31, 2014	May. 31, 2015	May. 31, 2014
Condensed Consolidated Statements Of Operations [Abstract]
Operating revenues	$ 160,707	$ 169,936	$ 436,641	$ 470,411
Cost of operating revenues	114,321	121,687	313,785	339,339
Gross profit	46,386	48,249	122,856	131,072
Operating expenses:
Selling expense	10,682	9,954	30,330	29,244
General and administrative expense	10,719	10,002	35,270	31,099
Engineering and research expense	3,497	3,071	9,330	8,602
Total operating expenses	24,898	23,027	74,930	68,945
Operating income	21,488	25,222	47,926	62,127
Other income (expense):
Interest expense	(1,144)	(45)	(1,424)	(140)
Interest income	134	295	468	587
Other expense, net	(55)	28	(748)	(468)
Earnings before income taxes	20,423	25,500	46,222	62,106
Income tax expense	7,496	9,001	16,732	21,923
Net earnings	$ 12,927	$ 16,499	$ 29,490	$ 40,183
Earnings per share:
Basic	$ 1.11	$ 1.28	$ 2.46	$ 3.12
Diluted	$ 1.10	$ 1.28	$ 2.46	$ 3.11
Shares used in computing earnings per share:
Basic	11,690	12,843	11,965	12,881
Diluted	11,720	12,889	12,000	12,927
Cash dividends declared per share	$ 0.270	$ 0.260	$ 0.810	$ 0.650