Concentrations - Additional Information (Detail)	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2018 Entity Agency Distributor	Sep. 30, 2017 Agency Distributor	Sep. 30, 2018 Entity Agency Distributor	Sep. 30, 2017 Agency Distributor	Dec. 31, 2017 Agency
Concentration Risk [Line Items]
Number of financial institutions | Entity	2		2
Number of distribution partners that were paid revenue | Distributor	0	0	0	0
Minimum
Concentration Risk [Line Items]
Percentage of revenue as criteria for major distribution partners	10.00%	10.00%	10.00%	10.00%
Revenue | Customer Concentration Risk
Concentration Risk [Line Items]
Number of advertising agencies	1	1	1	1
Concentration risk, percentage	12.00%		15.00%
Revenue | Customer Concentration Risk | Maximum
Concentration Risk [Line Items]
Concentration risk, percentage		10.00%		10.00%
Accounts Receivable | Customer Concentration Risk
Concentration Risk [Line Items]
Number of advertising agencies			1		1
Concentration risk, percentage			22.00%		21.00%
Accounts Receivable | Customer Concentration Risk | Other Advertising Agency
Concentration Risk [Line Items]
Concentration risk, percentage					11.00%
Accounts Receivable | Customer Concentration Risk | Other Advertising Agency | Maximum
Concentration Risk [Line Items]
Concentration risk, percentage			10.00%