CONDENSED CONSOLIDATED STATEMENT OF STOCKHOLDERS' EQUITY (Unaudited) - 6 months ended Mar. 31, 2016 - 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	$ 1,152,789	$ (2,033,644)	$ 1,368,255	$ (50,715)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Share-based compensation	28,300		28,300
Issuance of treasury stock under employee stock plans (in shares)		608
Issuance of treasury stock under employee stock plans	(19,124)	$ 6	(40,787)	21,657
Tax effect from share-based payment arrangements	13,508		13,508
Repurchases of common stock (shares)		(739)
Repurchases of common stock	(68,390)	$ (7)		(68,383)
Dividends paid	(1,245)				(1,245)
Net income	42,357				42,357
Foreign currency translation adjustments	(7,024)					(7,024)
Ending Balance (in shares) at Mar. 31, 2016		31,159
Ending Balance at Mar. 31, 2016	$ 425,380	$ 312	$ 1,153,810	$ (2,080,370)	$ 1,409,367	$ (57,739)