Nature of Operations and Summary of Significant Accounting Policies - Additional Information (Detail)	3 Months Ended		9 Months Ended
	Jun. 30, 2018 USD ($) patent institution $ / shares	Jun. 30, 2017 USD ($)	Jun. 30, 2018 USD ($) patent segment institution $ / shares	Jun. 30, 2017 USD ($)	Oct. 01, 2017 USD ($)	Sep. 30, 2017 USD ($) $ / shares
Accounting Policies [Abstract]
Number of financial institutions signed agreements to deploy mobile deposit (more than) (in institutions) | institution	6,100		6,100
Number of top retail banks that deployed mobile deposit | institution	50		50
Number of patents granted | patent	47		47
Number of pending patent applications | patent	20		20
Foreign currency translation adjustment	$ (942,000)	$ 318,000	$ (350,000)	$ 22,000
Other-than-temporary impairment charges recognized	0	$ 0	0	$ 0
Allowance for doubtful accounts receivable	234,000		234,000			$ 31,000
Software development costs capitalized	$ 0		0			$ 0
Capitalized software development costs for internal use software during period			$ 600,000
Number of operating segments | segment			1
Number of reporting units | segment			1
Common stock, par value (in dollars per share) | $ / shares	$ 0.001		$ 0.001			$ 0.001
Accumulated other comprehensive loss	$ 231,000		$ 231,000			$ (147,000)
Retained Earnings | ASU 2016-09
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect of new accounting principle in period of adoption					$ 8,300,000