CONSOLIDATED STATEMENTS OF CHANGES IN STOCKHOLDERS EQUITY - USD ($) $ in Thousands	Common Stock	Additional Paid-In Capital	Accumulated Other Comprehensive Income (Loss)	Accumulated Deficit	Treasury Stock	Total
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
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				(22,127)		(22,127)
Foreign currency translation adjustments			7,484			7,484
Changes in unrealized losses on marketable securities, net of tax effects			7			7
Actuarial loss, net of tax effects			(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
Beginning Balance at Mar. 31, 2020	$ 872	1,932,893	7,299	(578,975)	(200,956)	1,161,133
Beginning Balance (in shares) at Mar. 31, 2020	87,214,622
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Shares issued under restricted stock and purchase plans, net		1				1
Shares issued under restricted stock and purchase plans, net (in shares)	7,493
Stock-based compensation		3,725				3,725
Common stock dividends declared				(7,380)		(7,380)
Foreign currency translation adjustments			3,691			3,691
Actuarial loss, net of tax effects			(13)			(13)
Net income				13,696		13,696
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
Beginning Balance at Sep. 30, 2020	$ 873	1,942,850	21,919	(551,072)	(200,956)	$ 1,213,614
Beginning 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	2,578				$ 2,583
Shares issued under restricted stock and purchase plans, net (in shares)	464,888
Stock-based compensation		20,277				20,277
Common stock dividends declared				(22,287)		(22,287)
Foreign currency translation adjustments			4,720			4,720
Actuarial loss, net of tax effects			(20)			(20)
Net income				88,942		88,942
Ending Balance at Jun. 30, 2021	$ 878	1,965,705	26,619	(484,417)	(200,956)	$ 1,307,829
Ending Balance (in shares) at Jun. 30, 2021	87,758,598					74,296,729
Beginning Balance at Mar. 31, 2021	$ 878	1,959,619	22,637	(516,152)	(200,956)	$ 1,266,026
Beginning Balance (in shares) at Mar. 31, 2021	87,755,666
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Shares issued under restricted stock and purchase plans, net (in shares)	2,932
Stock-based compensation		6,086				6,086
Common stock dividends declared				(7,431)		(7,431)
Foreign currency translation adjustments			4,003			4,003
Actuarial loss, net of tax effects			(21)			(21)
Net income				39,166		39,166
Ending Balance at Jun. 30, 2021	$ 878	$ 1,965,705	$ 26,619	$ (484,417)	$ (200,956)	$ 1,307,829
Ending Balance (in shares) at Jun. 30, 2021	87,758,598					74,296,729