CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (LOSS) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Statement of Comprehensive Income [Abstract]
Net income (loss)	$ 62,612	$ (69,476)	$ 14,221
Other comprehensive income (loss), net of tax:
Cumulative foreign currency translation adjustments	(221)	8,844	(9,557)
Unrealized gains (losses) on marketable securities, net of tax effects of $0, $58 and $(83) for fiscal years 2017, 2016 and 2015	2	(106)	141
Actuarial gains (losses) arising in the year, net of tax effects of $(74), $161, and $115 for fiscal years 2017, 2016 and 2015, respectively	525	(322)	(605)
Pension settlement	(259)		232
Pension curtailment		852
Total other comprehensive income (loss), net of tax	47	9,268	(9,789)
Comprehensive income (loss)	$ 62,659	$ (60,208)	$ 4,432