Description of Business and Significant Accounting Policies - Revenue Recognition (Details) - USD ($)	3 Months Ended		12 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019
Description Of Business And Significant Accounting Policies [Line Items]
Unbilled receivables, current	$ 2,200,000		$ 2,000,000
Deferred commissions balance, beginning of period	17,902,000	$ 17,331,000	17,331,000
Deferral of commissions earned	3,664,000	4,056,000
Recognition of commission expense	(4,596,000)	(3,929,000)
Impairment of deferred commissions	(5,000)	(93,000)
Deferred commissions balance, end of period	16,965,000	$ 17,365,000	17,902,000
Other assets
Description Of Business And Significant Accounting Policies [Line Items]
Unbilled receivables, noncurrent	761,000		795,000
Unbilled
Description Of Business And Significant Accounting Policies [Line Items]
Accounts receivable	$ 2,166,000		$ 2,043,000
Minimum
Description Of Business And Significant Accounting Policies [Line Items]
Payment terms	30 days
Maximum
Description Of Business And Significant Accounting Policies [Line Items]
Payment terms	60 days
Total revenue | Product | Appliance | Maximum
Description Of Business And Significant Accounting Policies [Line Items]
Concentration risk, percentage	1.00%