CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Statement of Comprehensive Income [Abstract]
Net income	$ 22,606	$ 17,350	$ 106,112	$ 45,226
Other comprehensive income (loss), net of tax:
Cumulative foreign currency translation adjustments	(5,998)	4,592	3,288	(164)
Unrealized gains (losses) on marketable securities, net of tax effects of ($26) during each of the three and nine months ended June 30, 2018, and $0 during each of the three and nine months ended June 30, 2017	(122)	4	(122)	2
Actuarial gains (losses), net of tax effects of ($1) and ($3) during the three and nine months ended June 30, 2018, respectively, $0 and $5 during the three and nine months ended June 30, 2017, respectively	(3)	2	(6)	(4)
Total other comprehensive income (loss), net of tax	(6,123)	4,598	3,160	(166)
Comprehensive loss attributable to noncontrolling interest	111		111
Comprehensive income	$ 16,594	$ 21,948	$ 109,383	$ 45,060