Stockholders' Equity - Stock Option Activity (Details) - $ / shares	3 Months Ended	12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018
Number of Shares
Outstanding, Beginning Balance (in shares)	2,806,364
Granted (in shares)	364,368
Exercised (in shares)	(134,727)
Canceled (in shares)	(3,345)
Outstanding, Ending Balance (in shares)	3,032,660	2,806,364
Weighted-Average Exercise Price
Outstanding, Beginning Balance (in dollars per share)	$ 4.75
Granted (in dollars per share)	9.50
Exercised (in dollars per share)	4.35
Canceled (in dollars per share)	4.27
Outstanding, Ending Balance (in dollars per share)	$ 4.94	$ 4.75
Weighted-Average Remaining Contractual Term (in Years)
Outstanding (in years)	5 years 3 months 18 days	4 years 7 months 6 days