CONDENSED CONSOLIDATED STATEMENT OF STOCKHOLDERS' EQUITY - USD ($) shares in Thousands, $ in Thousands	Total	Common Stock	Additional Paid-in Capital	Treasury Stock	Retained Earnings	Accumulated Other Comprehensive Loss
Beginning Balance (in shares) at Sep. 30, 2020		29,096
Beginning Balance at Sep. 30, 2020	$ 331,082	$ 291	$ 1,218,583	$ (2,997,856)	$ 2,193,059	$ (82,995)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Share-based compensation	25,132		25,132
Issuance of treasury stock under employee stock plans (in shares)		241
Issuance of treasury stock under employee stock plans	(85,622)	$ 2	(97,822)	12,198
Repurchases of common stock (in shares)		(101)
Repurchases of common stock	(50,011)	$ (1)		(50,010)
Net income	86,492				86,492
Foreign currency translation adjustments	17,048					17,048
Ending Balance (in shares) at Dec. 31, 2020		29,236
Ending Balance at Dec. 31, 2020	324,121	$ 292	1,145,893	(3,035,668)	2,279,551	(65,947)
Beginning Balance (in shares) at Sep. 30, 2021		27,568
Beginning Balance at Sep. 30, 2021	(110,942)	$ 276	1,237,348	(3,857,855)	2,585,143	(75,854)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Share-based compensation	29,878		29,878
Issuance of treasury stock under employee stock plans (in shares)		185
Issuance of treasury stock under employee stock plans	(46,474)	$ 1	(58,861)	12,386
Repurchases of common stock (in shares)		(1,244)
Repurchases of common stock	(493,582)	$ (12)		(493,570)
Net income	84,959				84,959
Foreign currency translation adjustments	(2,138)					(2,138)
Ending Balance (in shares) at Dec. 31, 2021		26,509
Ending Balance at Dec. 31, 2021	$ (538,299)	$ 265	$ 1,208,365	$ (4,339,039)	$ 2,670,102	$ (77,992)