CONSOLIDATED STATEMENTS OF CHANGES IN 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, 2018	$ 841	$ 1,898,434	$ 13,587	$ (994,074)	$ (200,956)	$ 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	$ 15	1,533				1,548
Shares issued under restricted stock and purchase plans, net (in shares)	1,429,052
Stock-based compensation		9,717				9,717
Common stock dividends declared, at $0.20 per share				(14,428)		(14,428)
Foreign currency translation adjustments			(1,836)			(1,836)
Changes in unrealized gains (losses) on marketable securities, net of tax effects of $0 during the six months ended March 31, 2020 and March 31, 2019, respectively			111			111
Actuarial losses, net of tax effects $2 during the six months ended March 31, 2020, $3 during the six months ended March 31, 2019			(10)			(10)
Cumulative effect of adoption of ASC 606				(859)		(859)
Net income				17,836		17,836
Ending Balance at Mar. 31, 2019	$ 856	1,909,684	11,852	(991,525)	(200,956)	729,911
Ending Balance (in shares) at Mar. 31, 2019	85,593,182
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	2,315				$ 2,330
Shares issued under restricted stock and purchase plans, net (in shares)	1,454,922
Stock-based compensation		8,624				8,624
Common stock dividends declared, at $0.20 per share				(14,747)		(14,747)
Foreign currency translation adjustments			3,793			3,793
Changes in unrealized gains (losses) on marketable securities, net of tax effects of $0 during the six months ended March 31, 2020 and March 31, 2019, respectively			7			7
Actuarial losses, net of tax effects $2 during the six months ended March 31, 2020, $3 during the six months ended March 31, 2019			(12)			(12)
Net income				22,184		22,184
Ending Balance at Mar. 31, 2020	$ 872	$ 1,932,893	$ 7,299	$ (578,975)	$ (200,956)	$ 1,161,133
Ending Balance (in shares) at Mar. 31, 2020	87,214,622					73,752,753