Consolidated Statements of Stockholders' Equity - USD ($) shares in Thousands, $ in Thousands	Total	Common Stock	Additional Paid-in Capital	Retained Earnings	Accumulated Other Comprehensive Loss	Noncontrolling Interest
Beginning balance (in shares) at Sep. 30, 2017		54,398
Beginning balance at Sep. 30, 2017	$ 656,355	$ 544	$ 348,532	$ 347,885	$ (38,157)	$ (2,449)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock compensation	10,711		10,711
Release of restricted stock (in shares)		187
Release of restricted stock	2	$ 2
Taxes paid related to net share settlement of equity awards	(311)		(311)
Reclassification of stranded tax effects resulting from the Tax Cuts and Jobs Act	0			1,455	(1,455)
Foreign currency translation (loss) gain	(2,638)				(2,744)	106
Equity classified conversion feature of 2024 Convertible Notes, net of tax	38,995		38,995
Net income (loss)	36,294			37,282		(988)
Ending balance (in shares) at Sep. 30, 2018		54,585
Ending balance at Sep. 30, 2018	739,408	$ 546	397,927	386,622	(42,356)	(3,331)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock compensation	9,794		9,794
Release of restricted stock (in shares)		950
Release of restricted stock	10	$ 10
Taxes paid related to net share settlement of equity awards	(3,288)		(3,288)
Transfer of subsidiary shares to noncontrolling interest	0		3,195			(3,195)
Foreign currency translation (loss) gain	(10,042)				(10,042)
Deconsolidation of subsidiary	7,756					7,756
Net income (loss)	1,311			2,541		(1,230)
Ending balance (in shares) at Sep. 30, 2019		55,535
Ending balance at Sep. 30, 2019	744,949	$ 556	407,628	389,163	(52,398)	0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock compensation	(5,094)		(5,094)
Release of restricted stock (in shares)		711
Release of restricted stock	6	$ 6
Taxes paid related to net share settlement of equity awards	(1,435)		(1,435)
Foreign currency translation (loss) gain	(15,678)		0	(8)	(15,670)
Purchase and retirement of treasury shares (in shares)		(943)
Purchase and retirement of treasury stock	(5,158)	$ (11)	(2,624)	(2,523)
Net income (loss)	(68,463)			(68,463)		0
Ending balance (in shares) at Sep. 30, 2020		55,303
Ending balance at Sep. 30, 2020	$ 649,127	$ 551	$ 398,475	$ 318,169	$ (68,068)	$ 0