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	53,338		53,338
Issuance of treasury stock under employee stock plans (in shares)		275
Issuance of treasury stock under employee stock plans	(76,263)	$ 2	(90,229)	13,964
Repurchases of common stock (in shares)		(542)
Repurchases of common stock	(255,222)	$ (5)		(255,217)
Net income	155,166				155,166
Foreign currency translation adjustments	15,202					15,202
Ending Balance (in shares) at Mar. 31, 2021		28,829
Ending Balance at Mar. 31, 2021	223,303	$ 288	1,181,692	(3,239,109)	2,348,225	(67,793)
Beginning Balance (in shares) at Dec. 31, 2020		29,236
Beginning Balance at Dec. 31, 2020	324,121	$ 292	1,145,893	(3,035,668)	2,279,551	(65,947)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Share-based compensation	28,206		28,206
Issuance of treasury stock under employee stock plans (in shares)		34
Issuance of treasury stock under employee stock plans	9,359	$ 0	7,593	1,766
Repurchases of common stock (in shares)		(441)
Repurchases of common stock	(205,211)	$ (4)		(205,207)
Net income	68,674				68,674
Foreign currency translation adjustments	(1,846)					(1,846)
Ending Balance (in shares) at Mar. 31, 2021		28,829
Ending Balance at Mar. 31, 2021	223,303	$ 288	1,181,692	(3,239,109)	2,348,225	(67,793)
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	57,814		57,814
Issuance of treasury stock under employee stock plans (in shares)		237
Issuance of treasury stock under employee stock plans	(36,732)	$ 2	(52,882)	16,148
Repurchases of common stock (in shares)		(1,823)
Repurchases of common stock	(757,553)	$ (18)		(757,535)
Net income	189,342				189,342
Foreign currency translation adjustments	(5,345)					(5,345)
Ending Balance (in shares) at Mar. 31, 2022		25,982
Ending Balance at Mar. 31, 2022	(663,416)	$ 260	1,242,280	(4,599,242)	2,774,485	(81,199)
Beginning Balance (in shares) at Dec. 31, 2021		26,509
Beginning Balance at Dec. 31, 2021	(538,299)	$ 265	1,208,365	(4,339,039)	2,670,102	(77,992)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Share-based compensation	27,936		27,936
Issuance of treasury stock under employee stock plans (in shares)		52
Issuance of treasury stock under employee stock plans	9,742	$ 1	5,979	3,762
Repurchases of common stock (in shares)		(579)
Repurchases of common stock	(263,971)	$ (6)		(263,965)
Net income	104,383				104,383
Foreign currency translation adjustments	(3,207)					(3,207)
Ending Balance (in shares) at Mar. 31, 2022		25,982
Ending Balance at Mar. 31, 2022	$ (663,416)	$ 260	$ 1,242,280	$ (4,599,242)	$ 2,774,485	$ (81,199)