Basis of Presentation and Significant Accounting Policies - Summary of Option Activity (Detail) - $ / shares	3 Months Ended	12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Options, Outstanding Beginning Balance (in shares)	2,029,741
Options, Granted (in shares)	197,850
Options, Exercised (in shares)	0
Options, Forfeited (in shares)	(52,032)
Options, Outstanding Ending Balance (in shares)	2,175,559	2,029,741
Options, Exercisable Ending Balance (in shares)	1,469,416
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Abstract]
Weighted Average Exercise Price, Outstanding Beginning Balance (in usd per share)	$ 7.04
Weighted Average Exercise Price, Granted (in usd per share)	0.67
Weighted Average Exercise Price, Exercised (in usd per share)	0.00
Weighted Average Exercise Price, Forfeited (in usd per share)	4.50
Weighted Average Exercise Price, Outstanding Ending Balance (in usd per share)	6.52	$ 7.04
Weighted Average Exercise Price, Exercisable Ending Balance
Weighted Average Remaining Contractual Period in Years, Outstanding Ending Balance	6 years 1 month 6 days	5 years
Weighted Average Remaining Contractual Period in Years, Granted	9 years 9 months 15 days
Weighted Average Remaining Contractual Period in Years, Exercised	1 day
Weighted Average Remaining Contractual Period in Years, Forfeited	4 years 7 months 6 days
Weighted Average Remaining Contractual Period in Years, Exercisable Ending Balance	4 years 9 months 18 days