CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY - USD ($) shares in Thousands, $ in Thousands	Total	Common Stock	Paid-in- Capital	Treasury Stock	Retained Earnings	Accumulated Other Comprehensive Loss
Beginning Balance (in shares) at Sep. 30, 2015		31,290
Beginning Balance at Sep. 30, 2015	$ 436,998	$ 313	$ 1,156,626	$ (2,033,644)	$ 1,364,418	$ (50,715)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Share-based compensation	55,509		55,509
Issuance of treasury stock under employee stock plans (in shares)		980
Issuance of treasury stock under employee stock plans	(12,127)	$ 10	(47,406)	35,269
Tax effect from share-based payment arrangements	24,184		24,184
Repurchases of common stock (in shares)		(1,335)
Repurchases of common stock	(138,399)	$ (14)		(138,385)
Dividends paid	(2,489)				(2,489)
Net income	109,448				109,448
Foreign currency translation adjustments	(26,296)					(26,296)
Ending Balance (in shares) at Sep. 30, 2016		30,935
Ending Balance at Sep. 30, 2016	446,828	$ 309	1,188,913	(2,136,760)	1,471,377	(77,011)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Share-based compensation	61,222		61,222
Issuance of treasury stock under employee stock plans (in shares)		774
Issuance of treasury stock under employee stock plans	(25,758)	$ 8	(54,704)	28,938
Repurchases of common stock (in shares)		(1,466)
Repurchases of common stock	(193,290)	$ (15)		(193,275)
Dividends paid	(1,238)				(1,238)
Net income	128,256				128,256
Foreign currency translation adjustments	10,517					10,517
Ending Balance (in shares) at Sep. 30, 2017		30,243
Ending Balance at Sep. 30, 2017	426,537	$ 302	1,195,431	(2,301,097)	1,598,395	(66,494)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Share-based compensation	74,814		74,814
Issuance of treasury stock under employee stock plans (in shares)		633
Issuance of treasury stock under employee stock plans	(33,181)	$ 7	(59,194)	26,006
Repurchases of common stock (in shares)		(1,861)
Repurchases of common stock	(336,935)	$ (19)		(336,916)
Net income	142,415				142,415
Foreign currency translation adjustments	(9,913)					(9,913)
Ending Balance (in shares) at Sep. 30, 2018		29,015
Ending Balance at Sep. 30, 2018	$ 263,737	$ 290	$ 1,211,051	$ (2,612,007)	$ 1,740,810	$ (76,407)