Condensed Consolidated Statements Of Earnings - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	May 31, 2018	May 31, 2017	May 31, 2018	May 31, 2017
Income Statement [Abstract]
Operating revenues	$ 169,571	$ 151,533	$ 424,436	$ 386,048
Cost of operating revenues	118,093	105,627	305,245	278,827
Gross profit	51,478	45,906	119,191	107,221
Operating expenses:
Selling expense	10,842	10,451	31,087	30,565
General and administrative expense	17,974	13,693	44,203	35,278
Engineering and research expense	3,960	4,348	11,932	12,707
Total operating expenses	32,776	28,492	87,222	78,550
Operating income	18,702	17,414	31,969	28,671
Other income (expense):
Interest expense	(1,226)	(1,156)	(3,502)	(3,566)
Interest income	540	545	1,171	881
Other (expense) income, net	(571)	(606)	(1,725)	(818)
Earnings before income taxes	17,445	16,197	27,913	25,168
Income tax expense	7,066	5,245	12,614	8,331
Net earnings	$ 10,379	$ 10,952	$ 15,299	$ 16,837
Earnings per share:
Basic	$ 0.96	$ 1.03	$ 1.43	$ 1.58
Diluted	$ 0.96	$ 1.02	$ 1.42	$ 1.58
Shares used in computing earnings per share:
Basic	10,757	10,677	10,735	10,657
Diluted	10,785	10,705	10,763	10,682
Cash dividends declared per share	$ 0.30	$ 0.29	$ 0.90	$ 0.87