CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-In Capital	Accumulated Deficit	Accumulated Other Comprehensive Income (Loss)
Beginning Balance (in shares) at Sep. 30, 2016		32,782,000
Beginning 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		33,724,000
Ending Balance at Sep. 30, 2017	$ 61,408	$ 34	78,677	(17,450)	147
Increase (Decrease) in Stockholders' Equity [Roll Forward]
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
Stock-based compensation expense	8,950		8,950
Acquisition-related shares issued (in shares)		3,180,000
Acquisition-related shares issued	27,486	$ 3	27,483
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)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Exercise of stock options (in shares)	1,384,647	1,385,000
Exercise of stock options	$ 4,500	$ 1	4,499
Settlement of restricted stock units (in shares)		881,000
Settlement of restricted stock units	0	$ 1	(1)
Issuance of common stock under employee stock purchase plan (in shares)		140,000
Issuance of common stock under employee stock purchase plan	1,081		1,081
Stock-based compensation expense	9,637		9,637
Components of other comprehensive income (loss):
Net income (loss)	(724)			(724)
Currency translation adjustment	(3,504)				(3,504)
Change in unrealized gain (loss) on investments	29				29
Other comprehensive income (loss)	$ (4,199)
Ending Balance (in shares) at Sep. 30, 2019	40,367,456	40,367,000
Ending Balance at Sep. 30, 2019	$ 107,333	$ 40	$ 132,160	$ (20,806)	$ (4,061)