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	261,263				261,263
Other comprehensive income (loss)	(14,399)					(14,399)
Common stock issued for employee stock plans (in shares)		642,444
Common stock issued for employee stock plans	90,046	$ 7	90,039
Vesting of restricted stock (in shares)		75,530		27,852
Vesting of restricted stock	$ (6,155)			$ (6,155)
Repurchase of common stock (in shares)	664,945			664,945
Repurchases of common stock	$ (152,139)			$ (152,139)
Stock-based compensation expense	24,135		24,135
Dividends declared	(76,263)				(76,263)
Ending balance (in shares) at May. 31, 2019		39,982,823		1,765,060
Ending balance at May. 31, 2019	654,409	$ 400	781,705	$ (371,722)	309,147	(65,121)
Beginning balance (in shares) at Feb. 28, 2019		39,690,225		1,590,060
Beginning balance at Feb. 28, 2019	599,521	$ 397	732,538	$ (324,167)	244,388	(53,635)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	92,265				92,265
Other comprehensive income (loss)	(11,486)					(11,486)
Common stock issued for employee stock plans (in shares)		292,598
Common stock issued for employee stock plans	41,175	$ 3	41,172
Vesting of restricted stock	$ 0
Repurchase of common stock (in shares)	175,000			175,000
Repurchases of common stock	$ (47,555)			$ (47,555)
Stock-based compensation expense	7,995		7,995
Dividends declared	(27,506)				(27,506)
Ending balance (in shares) at May. 31, 2019		39,982,823		1,765,060
Ending balance at May. 31, 2019	654,409	$ 400	781,705	$ (371,722)	309,147	(65,121)
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	283,859				283,859
Other comprehensive income (loss)	(516)					(516)
Common stock issued for employee stock plans (in shares)		436,071		75
Common stock issued for employee stock plans	65,303	$ 5	65,318	$ (20)
Vesting of restricted stock (in shares)		16,657
Vesting of restricted stock	$ (1,581)			$ (1,581)
Repurchase of common stock (in shares)	657,136			657,136
Repurchases of common stock	$ (171,005)			$ (171,005)
Stock-based compensation expense	28,372		28,372
Dividends declared	(83,730)				(83,730)
Ending balance (in shares) at May. 31, 2020		40,556,920		2,649,793
Ending balance at May. 31, 2020	792,958	$ 406	900,663	$ (606,405)	573,354	(75,060)
Beginning balance (in shares) at Feb. 29, 2020		40,452,351		2,603,104
Beginning balance at Feb. 29, 2020	716,760	$ 405	875,488	$ (593,980)	501,326	(66,479)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	101,216				101,216
Other comprehensive income (loss)	(8,581)					(8,581)
Common stock issued for employee stock plans (in shares)		104,388		32
Common stock issued for employee stock plans	14,824	$ 1	14,832	$ (9)
Vesting of restricted stock (in shares)		181		21
Vesting of restricted stock	$ (6)			$ (6)
Repurchase of common stock (in shares)	46,636			46,636
Repurchases of common stock	$ (12,410)			$ (12,410)
Stock-based compensation expense	10,343		10,343
Dividends declared	(29,188)				(29,188)
Ending balance (in shares) at May. 31, 2020		40,556,920		2,649,793
Ending balance at May. 31, 2020	$ 792,958	$ 406	$ 900,663	$ (606,405)	$ 573,354	$ (75,060)