CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY - USD ($) $ in Thousands	Total	CommonStock	AdditionalPaid-InCapital	AccumulatedDeficit	AccumulatedOtherComprehensiveIncome (Loss)
Beginning Balance (in shares) at Sep. 30, 2015		31,721,000
Beginning Balance at Sep. 30, 2015	$ 30,433	$ 32	$ 63,905	$ (33,501)	$ (3)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Exercise of stock options (in shares)	661,663	662,000
Exercise of stock options	$ 1,755	$ 1	1,754
Settlement of restricted stock units (in shares)		262,000
Settlement of restricted stock units	0
Acquisition-related shares issued (in shares)		137,000
Acquisition-related shares issued	0
Stock-based compensation expense	4,079		4,079
Amortization of closing shares and earnout shares	1,298		1,298
Components of other comprehensive income (loss):
Net income (loss)	1,959			1,959
Currency translation adjustment	(46)				(46)
Change in unrealized gain (loss) on investments	7				7
Other comprehensive income (loss)	1,920
Ending Balance (in shares) at Sep. 30, 2016		32,782,000
Ending Balance at Sep. 30, 2016	$ 39,485	$ 33	71,036	(31,542)	(42)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Exercise of stock options (in shares)	235,514	235,000
Exercise of stock options	$ 687		687
Settlement of restricted stock units (in shares)		707,000
Settlement of restricted stock units	0	$ 1	(1)
Stock-based compensation expense	5,478		5,478
Amortization of closing shares and earnout shares	1,477		1,477
Components of other comprehensive income (loss):
Net income (loss)	14,092			14,092
Currency translation adjustment	208				208
Change in unrealized gain (loss) on investments	(19)				(19)
Other comprehensive income (loss)	$ 14,281
Ending Balance (in shares) at Sep. 30, 2017	33,724,392	33,724,000
Ending Balance at Sep. 30, 2017	$ 61,408	$ 34	78,677	(17,450)	147
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative-effect adjustment from the adoption of ASU 2016-09 | ASU 2016-09	$ 8,255			8,255
Exercise of stock options (in shares)	250,823	251,000
Exercise of stock options	$ 743		743
Settlement of restricted stock units (in shares)		745,000
Settlement of restricted stock units	0	$ 1	(1)
Issuance of common stock under employee stock purchase plan (in shares)		61,000
Issuance of common stock under employee stock purchase plan	382		382
Acquisition-related shares issued (in shares)		3,180,000
Acquisition-related shares issued	27,486	$ 3	27,483
Stock-based compensation expense	8,950		8,950
Amortization of closing shares and earnout shares	710		710
Components of other comprehensive income (loss):
Net income (loss)	(11,807)			(11,807)
Currency translation adjustment	(723)				(723)
Change in unrealized gain (loss) on investments	(10)				(10)
Other comprehensive income (loss)	$ (12,540)
Ending Balance (in shares) at Sep. 30, 2018	37,961,224	37,961,000
Ending Balance at Sep. 30, 2018	$ 95,394	$ 38	$ 116,944	$ (21,002)	$ (586)