Consolidated Statements of Changes in Stockholders' Equity - Unaudited - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-in Capital	Treasury Stock	Retained Earnings	Accumulated Other Comprehensive Loss
Beginning balance (in shares) at Aug. 31, 2018		39,264,849		1,072,263
Beginning balance at Aug. 31, 2018	$ 525,900	$ 393	$ 667,531	$ (213,428)	$ 122,843	$ (51,439)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	168,998				168,998
Other comprehensive income (loss)	(2,913)					(2,913)
Common stock issued for employee stock plans (in shares)		349,846
Common stock issued for employee stock plans	48,871	$ 4	48,867
Vesting of restricted stock (in shares)		75,530
Vesting of restricted stock	$ (6,155)			$ (6,155)
Repurchase of common stock (in shares)	489,945			489,945
Repurchases of common stock	$ (104,584)			$ (104,584)
Stock-based compensation expense	16,140		16,140
Dividends declared	(48,756)				(48,756)
Ending balance (in shares) at Feb. 28, 2019		39,690,225		1,590,060
Ending balance at Feb. 28, 2019	599,521	$ 397	732,538	$ (324,167)	244,388	(53,635)
Beginning balance (in shares) at Nov. 30, 2018		39,447,491		1,366,613
Beginning balance at Nov. 30, 2018	541,209	$ 394	694,078	$ (278,146)	184,071	(59,188)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	84,702				84,702
Other comprehensive income (loss)	5,553					5,553
Common stock issued for employee stock plans (in shares)		219,815
Common stock issued for employee stock plans	30,758	$ 3	30,755
Vesting of restricted stock (in shares)		22,919		8,502
Vesting of restricted stock	$ (1,878)			$ (1,878)
Repurchase of common stock (in shares)	214,945			214,945
Repurchases of common stock	$ (44,143)			$ (44,143)
Stock-based compensation expense	7,705		7,705
Dividends declared	(24,385)				(24,385)
Ending balance (in shares) at Feb. 28, 2019		39,690,225		1,590,060
Ending balance at Feb. 28, 2019	599,521	$ 397	732,538	$ (324,167)	244,388	(53,635)
Beginning balance (in shares) at Aug. 31, 2019		40,104,192		1,986,352
Beginning balance at Aug. 31, 2019	672,256	$ 401	806,973	$ (433,799)	373,225	(74,544)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	182,643				182,643
Other comprehensive income (loss)	8,065					8,065
Common stock issued for employee stock plans (in shares)		331,683		43
Common stock issued for employee stock plans	50,480	$ 4	50,487	$ (11)
Vesting of restricted stock (in shares)		16,476
Vesting of restricted stock	$ (1,575)			$ (1,575)
Repurchase of common stock (in shares)	610,500			610,500
Repurchases of common stock	$ (158,595)			$ (158,595)
Stock-based compensation expense	18,028		18,028
Dividends declared	(54,542)				(54,542)
Ending balance (in shares) at Feb. 29, 2020		40,452,351		2,603,104
Ending balance at Feb. 29, 2020	716,760	$ 405	875,488	$ (593,980)	501,326	(66,479)
Beginning balance (in shares) at Nov. 30, 2019		40,239,308		2,335,130
Beginning balance at Nov. 30, 2019	691,877	$ 402	835,968	$ (519,678)	439,891	(64,706)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	88,686				88,686
Other comprehensive income (loss)	(1,773)					(1,773)
Common stock issued for employee stock plans (in shares)		211,943		43
Common stock issued for employee stock plans	31,298	$ 3	31,306	$ (11)
Vesting of restricted stock (in shares)		1,100		431
Vesting of restricted stock	$ (119)			$ (119)
Repurchase of common stock (in shares)	267,500			267,500
Repurchases of common stock	$ (74,172)			$ (74,172)
Stock-based compensation expense	8,214		8,214
Dividends declared	(27,251)				(27,251)
Ending balance (in shares) at Feb. 29, 2020		40,452,351		2,603,104
Ending balance at Feb. 29, 2020	$ 716,760	$ 405	$ 875,488	$ (593,980)	$ 501,326	$ (66,479)