Condensed Consolidated Statements of Comprehensive (Loss) Income - USD ($) $ in Thousands	3 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Statement Of Income And Comprehensive Income [Abstract]
Net (loss) income	$ (1,556)	$ 2,300
Other comprehensive income (loss) :
Unrealized holding (losses) gains on available-for-sale securities, net of tax	(14)	46
Foreign currency translation adjustments	631	(2,254)
Other comprehensive income (loss)	617	(2,208)
Comprehensive (loss) income	$ (939)	$ 92