Consolidated Balance Sheets (Unaudited) (Parenthetical) - USD ($) shares in Thousands, $ in Thousands	Feb. 28, 2018	Aug. 31, 2017
Statement of Financial Position [Abstract]
Allowance for doubtful accounts	$ 10,419	$ 11,171
Accumulated depreciation	$ 474,073	$ 444,481
Common stock, par value	$ 1	$ 1
Common stock, shares authorized	75,000	75,000
Common stock, shares issued	48,585	48,529
Treasury stock, shares	19,060	19,063