Description of Business and Summary of Significant Accounting Policies (Narrative) (Detail) - USD ($)	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Depreciation and Amortization
Depreciation expense									$ 1,500,000	$ 1,700,000
Advertising Expense
Advertising expense									8,800,000	4,300,000
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	$ 22,179,000				$ 37,191,000				22,179,000	37,191,000	$ 53,596,000
Operating Income (Loss)	(5,883,000)	$ (6,265,000)	$ (9,391,000)	$ (10,904,000)	$ (5,556,000)	$ (4,928,000)	$ (6,833,000)	$ (4,954,000)	(32,443,000)	$ (22,271,000)
Cash	$ 16,800,000								$ 16,800,000
Equipment and Software | Minimum
Depreciation and Amortization
Useful life									3 years
Equipment and Software | Maximum
Depreciation and Amortization
Useful life									5 years