CONDENSED CONSOLIDATED STATEMENTS OF CHANGES IN SHAREHOLDERS' EQUITY - USD ($) shares in Thousands, $ in Thousands	Common Stock	Retained Earnings Cumulative effect of accounting standard adoption	Retained Earnings	Accumulated Other Comprehensive Loss	Treasury Stock	Noncontrolling Interest in VIE	Total
Balance at Sep. 30, 2019	$ 274,472	$ (824)	$ 862,948	$ (139,693)	$ (36,078)	$ 18,919
Balance (in shares) at Sep. 30, 2019							31,178
Increase (Decrease) in Stockholders' Equity
Net income (loss)			(59,698)			(9,188)	$ (59,698)
Other comprehensive income (loss), net of tax				(8,466)			$ (8,466)
Stock issued under equity incentive plans (in shares)							153
Stock issued under employee stock purchase plans, value	1,169
Stock issued under employee stock purchase plans (in shares)							19
Purchase of common stock, value	(3,660)
Purchase of common stock (in shares)							(54)
Share - based compensation	9,859
Cash dividends paid			(4,225)
Balance at Mar. 31, 2020	281,840		798,201	(148,159)	(36,078)	9,731
Balance (in shares) at Mar. 31, 2020							31,296
Balance at Dec. 31, 2019	276,497		841,549	(130,349)	(36,078)	22,909
Balance (in shares) at Dec. 31, 2019							31,274
Increase (Decrease) in Stockholders' Equity
Net income (loss)			(39,123)			(13,178)	$ (39,123)
Other comprehensive income (loss), net of tax				(17,810)			$ (17,810)
Stock issued under equity incentive plans (in shares)							23
Purchase of common stock, value	(39)
Purchase of common stock (in shares)							(1)
Share - based compensation	5,382
Cash dividends paid			(4,225)
Balance at Mar. 31, 2020	281,840		798,201	(148,159)	(36,078)	9,731
Balance (in shares) at Mar. 31, 2020							31,296
Balance at Sep. 30, 2020	295,986		850,472	(149,603)	(36,078)	27,403	$ 988,180
Balance (in shares) at Sep. 30, 2020							31,329
Increase (Decrease) in Stockholders' Equity
Net income (loss)			(49,012)			22,494	$ (49,012)
Other comprehensive income (loss), net of tax				17,195			$ 17,195
Stock issued under equity incentive plans (in shares)							556
Stock issued under employee stock purchase plans, value	1,170
Stock issued under employee stock purchase plans (in shares)							20
Purchase of common stock, value	(4,014)
Purchase of common stock (in shares)							(66)
Share - based compensation	11,151
Shares repurchased for tax withholdings					(5,243)
Shares repurchased for tax withholdings (in shares)							(86)
Cash dividends paid			(4,270)
Balance at Mar. 31, 2021	304,293		797,190	(132,408)	(41,321)	49,897	$ 977,651
Balance (in shares) at Mar. 31, 2021							31,753
Balance at Dec. 31, 2020	297,655		837,477	(138,296)	(36,078)	33,120
Balance (in shares) at Dec. 31, 2020							31,810
Increase (Decrease) in Stockholders' Equity
Net income (loss)			(36,017)			16,777	$ (36,017)
Other comprehensive income (loss), net of tax				5,888			$ 5,888
Stock issued under equity incentive plans (in shares)							9
Stock issued under employee stock purchase plans, value	1,170
Stock issued under employee stock purchase plans (in shares)							20
Purchase of common stock, value	(1,004)
Share - based compensation	6,472
Shares repurchased for tax withholdings					(5,243)
Shares repurchased for tax withholdings (in shares)							(86)
Cash dividends paid			(4,270)
Balance at Mar. 31, 2021	$ 304,293		$ 797,190	$ (132,408)	$ (41,321)	$ 49,897	$ 977,651
Balance (in shares) at Mar. 31, 2021							31,753