Nature of Operations and Summary of Significant Accounting Policies - Additional Information (Detail)	3 Months Ended
	Dec. 31, 2017 USD ($) patent segment institution	Dec. 31, 2016 USD ($)	Sep. 30, 2017 USD ($)	Oct. 01, 2016 USD ($)
Accounting Policies [Abstract]
Number of financial institutions signed agreements to deploy mobile deposit (more than) (in institutions) | institution	6,100
Number of top retail banks that deployed mobile deposit | institution	50
Number of patents granted | patent	35
Number of pending patent applications | patent	19
Foreign currency translation adjustment gains (losses)	$ 189,000	$ (370,000)
Other-than-temporary impairment charges recognized	0	0
Write-off of allowance for doubtful accounts	0	0
Allowance for doubtful accounts receivable	134,000		$ 31,000
Capitalized software development costs	54,000	0
Software development costs capitalized	0		0
Capitalized software development costs amortized	$ 0	$ 0
Number of operating segments (in segments) | segment	1
Number of reporting units (in segments) | segment	1
Accumulated other comprehensive income	$ 277,000		$ 147,000
Retained Earnings | Accounting Standards Update 2016-09
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Increase to retained earnings				$ 8,300,000