Warrants - Additional Information (Detail) $ / shares in Units, $ in Thousands			1 Months Ended	12 Months Ended
	Oct. 23, 2017 shares	Sep. 29, 2017 USD ($) WarrantHolder shares	May 31, 2016 USD ($) $ / shares shares	Dec. 31, 2017 USD ($) $ / shares shares	Dec. 31, 2015 USD ($) shares	Oct. 03, 2017 shares	Nov. 16, 2015 shares
Class Of Warrant Or Right [Line Items]
Fair value of shares sold with warrants | $			$ 44,700	$ 20,593	$ 8,253
Exercise price of warrants | $ / shares			$ 7.50	$ 13.05
Outstanding warrants				32,000			32,000
Adjustment of warrant liability | $		$ 1,900		$ 1,880
Common Stock
Class Of Warrant Or Right [Line Items]
Number of shares sold in underwritten public offering	973,236			173,000	1,788,000
Shares issuable under warrants granted						1,292,510
A Warrants
Class Of Warrant Or Right [Line Items]
Class of warrants expiration period upon issuance			2 years
B Warrants
Class Of Warrant Or Right [Line Items]
Class of warrants expiration period upon issuance			30 months
Warrants exercisable date			2017-05
Warrant Exchange Agreement
Class Of Warrant Or Right [Line Items]
Number of warrant holders | WarrantHolder		4
Outstanding warrants		9,700,000
Maximum | A Warrants
Class Of Warrant Or Right [Line Items]
Warrants to purchase of common stock			7,281,553
Maximum | B Warrants
Class Of Warrant Or Right [Line Items]
Warrants to purchase of common stock			2,427,184
Registered Offering
Class Of Warrant Or Right [Line Items]
Number of shares sold in underwritten public offering			9,708,737