Condensed Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	May 31, 2018	Aug. 31, 2017	May 31, 2017
Statement Of Financial Position [Abstract]
Receivables, allowance	$ 4,143	$ 7,447	$ 7,473
Preferred stock, par value	$ 1	$ 1	$ 1
Preferred stock, authorized	2,000,000	2,000,000	2,000,000
Preferred stock, issued	0	0	0
Preferred stock, outstanding	0	0	0
Common stock, par value	$ 1	$ 1	$ 1
Common stock, authorized	25,000,000	25,000,000	25,000,000
Common stock, issued	18,841,000	18,780,000	18,773,000
Treasury stock, shares	8,083,000	8,083,000	8,083,000