Stockholders' Equity - Stock Option Activity (Detail) - $ / shares	6 Months Ended	12 Months Ended
	Mar. 31, 2017	Sep. 30, 2016
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Number of Shares, Options Outstanding, Beginning Balance (in shares)	3,015,374
Number of Shares, Granted (in shares)	107,800
Number of Shares, Exercised (in shares)	(10,291)
Number of Shares, Canceled (in shares)	(32,501)
Number of Shares, Options Outstanding, Ending Balance (in shares)	3,080,382	3,015,374
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Abstract]
Weighted-Average Exercise Price, Outstanding, Beginning Balance (in dollars per share)	$ 3.95
Weighted-Average Exercise Price, Granted (in dollars per share)	6.13
Weighted-Average Exercise Price, Exercised (in dollars per share)	2.85
Weighted-Average Exercise Price, Canceled (in dollars per share)	4.29
Weighted-Average Exercise Price, Outstanding, Ending Balance (in dollars per share)	$ 4.02	$ 3.95
Share-based Compensation Arrangement by Share-based Payment Award, Options, Additional Disclosures [Abstract]
Weighted-Average Remaining Contractual Term, Outstanding (in years)	6 years	6 years 4 months 24 days