CONDENSED CONSOLIDATED STATEMENT OF STOCKHOLDERS' EQUITY - 6 months ended Mar. 31, 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	29,231		29,231
Issuance of treasury stock under employee stock plans (in shares)		633
Issuance of treasury stock under employee stock plans	(27,800)	$ 7	(51,371)	23,564
Repurchases of common stock (in shares)		(606)
Repurchases of common stock	(74,647)	$ (6)		(74,641)
Dividends paid	(1,238)				(1,238)
Net income	62,985				62,985
Foreign currency translation adjustments	(8,258)					(8,258)
Ending Balance (in shares) at Mar. 31, 2017		30,962
Ending Balance at Mar. 31, 2017	$ 427,101	$ 310	$ 1,162,936	$ (2,187,837)	$ 1,536,961	$ (85,269)