CoSense Joint Venture Agreement and Discontinued Operations - Components of Income of Discontinued Operations (Detail) - USD ($)	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Expenses
Net loss from discontinued operations		$ (514,000)
CoSense, NFI and Serenz [Member] | Discontinued Operations, Held-for-sale [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Product revenue		51,000
Cost of product revenue		51,000
Expenses
Research and development		401,000
Sales and marketing		11,000
General and administrative		102,000
Total expenses		514,000
Net loss from discontinued operations	$ 0	$ (514,000)