CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Statement of Comprehensive Income [Abstract]
Net income	$ 7,254	$ 22,606	$ 25,090	$ 106,112
Other comprehensive income (loss), net of tax:
Cumulative foreign currency translation adjustments	2,724	(5,998)	888	3,288
Unrealized gains (losses) on marketable securities, net of tax effects of $0 during each of the three and nine months ended June 30, 2019, and ($26) during each of the three and nine months ended June 30, 2018		(122)	111	(122)
Actuarial gains (losses), net of tax effects of ($3) and $0 during the three and nine months ended June 30, 2019, respectively, ($1) and ($3) during the three and nine months ended June 30, 2018, respectively	9	(3)		(6)
Total other comprehensive income (loss), net of tax	2,733	(6,123)	999	3,160
Comprehensive loss attributable to noncontrolling interest		111		111
Comprehensive income	$ 9,987	$ 16,594	$ 26,089	$ 109,383