CONSOLIDATED STATEMENTS OF COMPREHENSIVE LOSS (Unaudited) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2018	Mar. 31, 2017
Statement Of Income And Comprehensive Income [Abstract]
Net loss	$ (4,729)	$ (11,503)	$ (14,209)	$ (23,208)
Other comprehensive income (loss), net of tax
Change in unrealized gains (losses) on available-for-sale securities	(38)	11	(89)	(51)
Foreign currency translation adjustments	1,039	1,353	834	1,047
Total other comprehensive income, net of tax	1,001	1,364	745	996
Total comprehensive loss	$ (3,728)	$ (10,139)	$ (13,464)	$ (22,212)