Consolidated Statements of Comprehensive Loss - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Statement Of Income And Comprehensive Income [Abstract]
Net loss	$ (19,212)	$ (56,791)	$ (45,970)
Other comprehensive income (loss), net of tax:
Change in unrealized losses on available-for-sale securities	(24)	(43)	(12)
Foreign currency translation adjustments	(1,365)	1,754	(2,984)
Other comprehensive income (loss), net of tax	(1,389)	1,711	(2,996)
Total comprehensive loss	$ (20,601)	$ (55,080)	$ (48,966)