CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Thousands	3 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Statement of Comprehensive Income [Abstract]
Net income	$ 16,486	$ 13,871
Other comprehensive income (loss), net of tax:
Cumulative foreign currency translation adjustments	4,131	(10,103)
Unrealized losses on marketable securities, net of tax effects of $0 during each of the three months ended December 31, 2017 and 2016		(11)
Actuarial (losses) gains, net of tax effects of ($2), and $2 during the three months ended December 31, 2017 and 2016	(9)	11
Total other comprehensive income (loss), net of tax	4,122	(10,103)
Comprehensive income	$ 20,608	$ 3,768