CONSOLIDATED STATEMENTS OF CHANGES IN EQUITY - USD ($) $ in Thousands	Common Stock	Additional Paid-In Capital	Accumulated Other Comprehensive Income (Loss)	Accumulated Deficit Cumulative Effect, Period of Adoption, Adjustment	Accumulated Deficit	Treasury Stock	Cumulative Effect, Period of Adoption, Adjustment	Total
Beginning Balance at Sep. 30, 2018	$ 841	$ 1,898,434	$ 13,587	$ (859)	$ (994,074)	$ (200,956)	$ (859)	$ 717,832
Beginning Balance (in shares) at Sep. 30, 2018	84,164,130
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Shares issued under restricted stock and purchase plans, net	$ 16	1,532						1,548
Shares issued under restricted stock and purchase plans, net (in shares)	1,517,144
Stock-based compensation		15,172						15,172
Common stock dividends declared, at $0.30 per share					(21,656)			(21,656)
Foreign currency translation adjustments			888					888
Changes in unrealized gains (losses) on marketable securities, net of tax effects of $0			111					111
Net income					25,090			25,090
Ending Balance at Jun. 30, 2019	$ 857	1,915,138	14,586		(991,499)	(200,956)		738,126
Ending Balance (in shares) at Jun. 30, 2019	85,681,274
Beginning Balance at Sep. 30, 2019	$ 857	1,921,954	3,511		(586,412)	(200,956)		$ 1,138,954
Beginning Balance (in shares) at Sep. 30, 2019	85,759,700							72,297,831
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Shares issued under restricted stock and purchase plans, net	$ 15	2,317						$ 2,332
Shares issued under restricted stock and purchase plans, net (in shares)	1,462,415
Stock-based compensation		12,348						12,348
Common stock dividends declared, at $0.30 per share					(22,127)			(22,127)
Foreign currency translation adjustments			7,484					7,484
Changes in unrealized gains (losses) on marketable securities, net of tax effects of $0			7					7
Actuarial losses, net of tax effects of $4			(25)					(25)
Net income					35,880			35,880
Ending Balance at Jun. 30, 2020	$ 872	$ 1,936,619	$ 10,977		$ (572,659)	$ (200,956)		$ 1,174,853
Ending Balance (in shares) at Jun. 30, 2020	87,222,115							73,760,246