Summary of Significant Accounting Policies - Additional Information (Detail) - USD ($)	3 Months Ended
	Mar. 31, 2018	Dec. 31, 2017	Mar. 31, 2017
Significant Accounting Policies [Line Items]
Restricted cash deposit	$ 302,000	$ 65,000
Restricted cash	65,000	$ 65,000
Restricted cash noncurrent	237,000		$ 165,000
Income tax expense (benefit)	$ 0
2018 Omnibus Incentive Plan [Member]
Significant Accounting Policies [Line Items]
Number of shares authorized for common stock for equity awards	5,001,000