CONDENSED CONSOLIDATED STATEMENT OF STOCKHOLDERS' EQUITY (Unaudited) - 3 months ended Dec. 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, 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	14,519		14,519
Issuance of treasury stock under employee stock plans (in shares)		480
Issuance of treasury stock under employee stock plans	(31,935)	$ 5	(49,763)	17,823
Repurchases of common stock (shares)		(258)
Repurchases of common stock	(30,442)	$ (2)		(30,440)
Dividends paid	(618)				(618)
Net income	37,901				37,901
Foreign currency translation adjustments	(14,347)					(14,347)
Ending Balance (in shares) at Dec. 31, 2016		31,157
Ending Balance at Dec. 31, 2016	$ 421,906	$ 312	$ 1,149,832	$ (2,149,377)	$ 1,512,497	$ (91,358)