CONDENSED CONSOLIDATED STATEMENT OF STOCKHOLDERS' EQUITY - 9 months ended Jun. 30, 2018 - 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, 2017		30,243
Beginning 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	54,631		54,631
Issuance of treasury stock under employee stock plans (in shares)		433
Issuance of treasury stock under employee stock plans	(40,380)	$ 4	(57,740)	17,356
Repurchases of common stock (in shares)		(1,359)
Repurchases of common stock	(231,479)	$ (13)		(231,466)
Net income	91,935				91,935
Foreign currency translation adjustments	(6,600)					(6,600)
Ending Balance (in shares) at Jun. 30, 2018		29,317
Ending Balance at Jun. 30, 2018	$ 294,644	$ 293	$ 1,192,322	$ (2,515,207)	$ 1,690,330	$ (73,094)