CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Statement of Comprehensive Income [Abstract]
Net income (loss)	$ 116,464	$ 62,612	$ (69,476)
Other comprehensive (loss) income, net of tax:
Cumulative foreign currency translation adjustments	(1,651)	(221)	8,844
Unrealized (losses) gains on marketable securities, net of tax effects of $0, $0 and $58 for fiscal years 2018, 2017 and 2016	(111)	2	(106)
Actuarial gains (losses), net of tax effects of ($49), ($74) and $161 for fiscal years 2018, 2017 and 2016	136	525	(322)
Pension settlement		(259)
Pension curtailment			852
Total other comprehensive (loss) income, net of tax	(1,626)	47	9,268
Comprehensive loss attributable to noncontrolling interest	111
Comprehensive income (loss)	$ 114,949	$ 62,659	$ (60,208)