CONSOLIDATED STATEMENTS OF CHANGES IN STOCKHOLDERS EQUITY - USD ($) $ in Thousands	Common Stock	Additional Paid-In Capital	Accumulated Other Comprehensive Income	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	3,407						3,423
Shares issued under restricted stock and purchase plans, net (in shares)	1,595,570
Stock-based compensation		20,113						20,113
Common stock dividends declared					(28,895)			(28,895)
Net income					437,416			437,416
Foreign currency translation adjustments			(9,333)					(9,333)
Changes in unrealized losses on marketable securities, net of tax effects			104					104
Actuarial loss, net of tax effects			(847)					(847)
Ending Balance at Sep. 30, 2019	$ 857	1,921,954	3,511		(586,412)	(200,956)		1,138,954
Ending Balance (in shares) at Sep. 30, 2019	85,759,700
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Shares issued under restricted stock and purchase plans, net	$ 16	4,579						4,595
Shares issued under restricted stock and purchase plans, net (in shares)	1,534,010
Stock-based compensation		16,317						16,317
Common stock dividends declared					(29,513)			(29,513)
Net income					64,853			64,853
Foreign currency translation adjustments			18,877					18,877
Changes in unrealized losses on marketable securities, net of tax effects			7					7
Actuarial loss, net of tax effects			(476)					(476)
Ending Balance at Sep. 30, 2020	$ 873	1,942,850	21,919		(551,072)	(200,956)		$ 1,213,614
Ending Balance (in shares) at Sep. 30, 2020	87,293,710							73,831,841
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Shares issued under restricted stock and purchase plans, net	$ 5	5,806						$ 5,811
Shares issued under restricted stock and purchase plans, net (in shares)	515,212
Stock-based compensation		27,456						27,456
Common stock dividends declared					(29,726)			(29,726)
Net income					110,747			110,747
Foreign currency translation adjustments			(2,922)					(2,922)
Actuarial loss, net of tax effects			354					354
Ending Balance at Sep. 30, 2021	$ 878	$ 1,976,112	$ 19,351		$ (470,051)	$ (200,956)		$ 1,325,334
Ending Balance (in shares) at Sep. 30, 2021	87,808,922							74,347,053