Stockholders' Equity - Stock Option Activity (Details) - $ / shares	3 Months Ended	6 Months Ended
	Dec. 31, 2018	Mar. 31, 2019
Number of Shares
Outstanding, Beginning Balance (in shares)	2,806,364	2,806,364
Granted (in shares)		364,368
Exercised (in shares)		(637,051)
Canceled (in shares)		(143,562)
Outstanding, Ending Balance (in shares)		2,390,119
Weighted-Average Exercise Price
Outstanding, Beginning Balance (in dollars per share)	$ 4.75	$ 4.75
Granted (in dollars per share)		9.50
Exercised (in dollars per share)		3.38
Canceled (in dollars per share)		6.62
Outstanding, Ending Balance (in dollars per share)		$ 5.73
Weighted-Average Remaining Contractual Term (in Years)
Outstanding (in years)	4 years 7 months 6 days	5 years 3 months 18 days