QUARTERLY INFORMATION (UNAUDITED) (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended												12 Months Ended
	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Quarterly Financial Information Disclosure [Abstract]
Revenue	$ 21,037	$ 16,109	$ 14,277	$ 12,136	$ 12,904	$ 11,798	$ 11,419	$ 9,269	$ 9,670	$ 9,105	$ 8,522	$ 7,404
Cost of revenue	2,674	2,678	1,717	1,617	1,138	1,182	830	891	940	793	720	942
Operating expenses	19,729	16,294	13,825	12,831	10,033	10,132	9,365	9,050	7,889	7,618	7,171	6,804
Operating income (loss)	(1,366)	(2,863)	(1,265)	(2,312)	1,733	484	1,224	(672)	841	694	631	(342)	$ (7,806)	$ 2,769	$ 1,824
Other income (expense), net	22	(1,351)	204	190	121	149	67	65	23	45	30	36	(935)	402	134
Income tax benefit (provision)	(783)	1,430	(99)	(3,614)	11,012	(17)	(74)	0	96	0	(79)	(16)	(3,066)	10,921	1
Net income (loss)	$ (2,127)	$ (2,784)	$ (1,160)	$ (5,736)	$ 12,866	$ 616	$ 1,217	$ (607)	$ 960	$ 739	$ 582	$ (322)	$ (11,807)	$ 14,092	$ 1,959
Net income (loss) per share:
Net income (loss) per share—basic (in dollars per share)	$ (0.06)	$ (0.08)	$ (0.03)	$ (0.17)	$ 0.38	$ 0.02	$ 0.04	$ (0.02)	$ 0.03	$ 0.02	$ 0.02	$ (0.01)	$ (0.33)	$ 0.43	$ 0.06
Shares used in calculating net income (loss) per share—basic (in shares)	37,858	36,190	34,976	34,207	33,522	33,024	32,786	32,377	32,086	31,823	31,326	31,094	35,811	33,083	31,587
Net income (loss) per share—diluted (in dollars per share)	$ (0.06)	$ (0.08)	$ (0.03)	$ (0.17)	$ 0.35	$ 0.02	$ 0.03	$ (0.02)	$ 0.03	$ 0.02	$ 0.02	$ (0.01)	$ (0.33)	$ 0.40	$ 0.06
Shares used in calculating net income (loss) per share—diluted (in shares)	37,858	36,190	34,976	34,207	36,251	35,610	34,815	32,377	34,860	34,532	33,134	31,094	35,811	35,537	33,819