Nature of Operations and Summary of Significant Accounting Policies - Calculation of Basic and Diluted Net Loss Per Share (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2018	Mar. 31, 2017
Accounting Policies [Abstract]
Net income (loss)	$ (1,160)	$ 1,217	$ (6,896)	$ 610
Weighted-average shares outstanding - basic (in shares)	34,976	32,786	34,587	32,582
Common stock equivalents (in shares)	0	2,029	0	2,236
Weighted-average shares outstanding - diluted (in shares)	34,976	34,815	34,587	34,818
Net income (loss) per share:
Basic (in dollars per share)	$ (0.03)	$ 0.04	$ (0.20)	$ 0.02
Diluted (in dollars per share)	$ (0.03)	$ 0.03	$ (0.20)	$ 0.02