QUARTERLY INFORMATION (UNAUDITED) - SCHEDULE OF QUARTERLY FINANCIAL DATA (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended												12 Months Ended
	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, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Quarterly Financial Information Disclosure [Abstract]
Revenue	$ 12,904	$ 11,798	$ 11,419	$ 9,269	$ 9,670	$ 9,105	$ 8,522	$ 7,404	$ 7,866	$ 6,440	$ 5,672	$ 5,389	$ 45,390	$ 34,701	$ 25,367
Cost of revenue	1,138	1,182	830	891	940	793	720	942	825	591	558	497
Operating expenses	10,033	10,132	9,365	9,050	7,889	7,618	7,171	6,804	6,079	5,539	4,628	4,758
Operating income	1,733	484	1,224	(672)	841	694	631	(342)	962	310	486	134	2,769	1,824	1,892
Other income, net	121	149	67	65	23	45	30	36	25	30	21	15	402	134	91
Income tax benefit (provision)	11,012	(17)	(74)	0	96	0	(79)	(16)	(32)	578	0	(3)	10,921	1	543
Net income	$ 12,866	$ 616	$ 1,217	$ (607)	$ 960	$ 739	$ 582	$ (322)	$ 955	$ 918	$ 507	$ 146	$ 14,092	$ 1,959	$ 2,526
Net income (loss) per share:
Basic income (loss) per share (in dollars per share)	$ 0.38	$ 0.02	$ 0.04	$ (0.02)	$ 0.03	$ 0.02	$ 0.02	$ (0.01)	$ 0	$ 0.03	$ 0.02	$ 0.00	$ 0.43	$ 0.06	$ 0.08
Shares used in calculating net income per share—basic	33,522	33,024	32,786	32,377	32,086	31,823	31,326	31,094	30,969	30,765	30,697	30,618	33,083	31,587	30,790
Diluted income (loss) per share (in dollars per share)	$ 0.35	$ 0.02	$ 0.03	$ (0.02)	$ 0.03	$ 0.02	$ 0.02	$ (0.01)	$ 0	$ 0.03	$ 0.02	$ 0.00	$ 0.40	$ 0.06	$ 0.08
Shares used in calculating net income (loss) per share - diluted	36,251	35,610	34,815	32,377	34,860	34,532	33,134	31,094	31,664	31,646	31,321	31,174	35,537	33,819	31,480