CONDENSED CONSOLIDATED STATEMENT OF STOCKHOLDERS' EQUITY - 9 months ended Jun. 30, 2017 - 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, 2016		30,935
Beginning Balance at Sep. 30, 2016	$ 446,828	$ 309	$ 1,185,076	$ (2,136,760)	$ 1,475,214	$ (77,011)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Share-based compensation	43,546		43,546
Issuance of treasury stock under employee stock plans (in shares)		731
Issuance of treasury stock under employee stock plans	(26,212)	$ 7	(53,504)	27,285
Repurchases of common stock (in shares)		(946)
Repurchases of common stock	(120,518)	$ (9)		(120,509)
Dividends paid	(1,238)				(1,238)
Net income	88,212				88,212
Foreign currency translation adjustments	2,137					2,137
Ending Balance (in shares) at Jun. 30, 2017		30,720
Ending Balance at Jun. 30, 2017	$ 432,755	$ 307	$ 1,175,118	$ (2,229,984)	$ 1,562,188	$ (74,874)