CONSOLIDATED STATEMENTS OF CHANGES IN STOCKHOLDERS EQUITY - USD ($) $ in Thousands	Common Stock	Additional Paid-In Capital	Accumulated Other Comprehensive Income	Accumulated Deficit	Treasury Stock	Total
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
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)	461,956
Stock-based compensation		14,191				14,191
Common stock dividends declared				(14,856)		(14,856)
Foreign currency translation adjustments			717			717
Actuarial loss, net of tax effects			1			1
Net income				49,776		49,776
Ending Balance at Mar. 31, 2021	$ 878	1,959,619	22,637	(516,152)	(200,956)	1,266,026
Ending Balance (in shares) at Mar. 31, 2021	87,755,666
Beginning Balance at Dec. 31, 2020	$ 877	1,949,556	35,145	(532,468)	(200,956)	1,252,154
Beginning Balance (in shares) at Dec. 31, 2020	87,672,132
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Shares issued under restricted stock and purchase plans, net	$ 1	2,582				2,583
Shares issued under restricted stock and purchase plans, net (in shares)	83,534
Stock-based compensation		7,481				7,481
Common stock dividends declared				(7,432)		(7,432)
Foreign currency translation adjustments			(12,547)			(12,547)
Actuarial loss, net of tax effects			39			39
Net income				23,748		23,748
Ending Balance at Mar. 31, 2021	$ 878	1,959,619	22,637	(516,152)	(200,956)	1,266,026
Ending Balance (in shares) at Mar. 31, 2021	87,755,666
Beginning Balance at Sep. 30, 2021	$ 878	1,976,112	19,351	(470,051)	(200,956)	$ 1,325,334
Beginning Balance (in shares) at Sep. 30, 2021	87,808,922					74,347,053
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Shares issued under restricted stock and purchase plans, net	$ 7	3,455				$ 3,462
Shares issued under restricted stock and purchase plans, net (in shares)	641,161
Stock-based compensation		7,229				7,229
Common stock dividends declared				(7,493)		(7,493)
Net investment hedge currency translation adjustment			10,673			10,673
Foreign currency translation reclassification adjustments included in income from discontinued operation (Note 2)			(16,567)			(16,567)
Foreign currency translation adjustments			(17,630)			(17,630)
Changes in unrealized gains on marketable securities, net of tax			(3,306)			(3,306)
Actuarial loss, net of tax effects			81			81
Net income				2,163,193		2,163,193
Ending Balance at Mar. 31, 2022	$ 885	1,986,796	(7,398)	1,685,649	(200,956)	$ 3,464,976
Ending Balance (in shares) at Mar. 31, 2022	88,450,083					74,983,621
Beginning Balance at Dec. 31, 2021	$ 884	1,977,571	24,149	(434,225)	(200,956)	$ 1,367,423
Beginning Balance (in shares) at Dec. 31, 2021	88,375,410
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Shares issued under restricted stock and purchase plans, net	$ 1	3,460				3,461
Shares issued under restricted stock and purchase plans, net (in shares)	74,673
Stock-based compensation		5,765				5,765
Net investment hedge currency translation adjustment			10,673			10,673
Foreign currency translation reclassification adjustments included in income from discontinued operation (Note 2)			(16,567)			(16,567)
Foreign currency translation adjustments			(22,431)			(22,431)
Changes in unrealized gains on marketable securities, net of tax			(3,306)			(3,306)
Actuarial loss, net of tax effects			84			84
Net income				2,119,874		2,119,874
Ending Balance at Mar. 31, 2022	$ 885	$ 1,986,796	$ (7,398)	$ 1,685,649	$ (200,956)	$ 3,464,976
Ending Balance (in shares) at Mar. 31, 2022	88,450,083					74,983,621