Preferred Stock Warrant Liability - Additional Information (Detail) - USD ($)	1 Months Ended	12 Months Ended
	Jul. 31, 2008	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Jan. 31, 2014
Class of Warrant or Right [Line Items]
Gains (losses) on fair value of warrants			$ (82,000)	$ (10,000)
Common Stock [Member]
Class of Warrant or Right [Line Items]
Shares of common stock issued in net settlement of warrant exercise		4,349
Series A Preferred Stock [Member]
Class of Warrant or Right [Line Items]
Exercise price					$ 1.00
Fair value of warrants		$ 100,000
Series A Preferred Stock [Member] | Maximum [Member]
Class of Warrant or Right [Line Items]
Gains (losses) on fair value of warrants			$ 100,000	$ 100,000
Series A Preferred Stock [Member] | Warrant [Member]
Class of Warrant or Right [Line Items]
Exercised shares	160,000
Exercise price	$ 1.00
Shares exercised period	10 years