Description of Business and Basis of Preparation - Additional Information (Detail)	Sep. 14, 2018 USD ($) $ / shares shares
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]
Shelf registration maximum equity offering price | $	$ 175,000,000
Number of warrants issued to purchase common stock (in shares)	13,198,075
Aggregate amount receivable upon exercise of warrants | $	$ 28,600,000
Warrants, expiration date	Mar. 14, 2019
Sales Agreement | Common Stock
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]
Shelf registration maximum equity offering price | $	$ 25,000,000
June 2016 Public Offering
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]
Number of warrants issued to purchase common stock (in shares)	4,218,750
Exercise price of warrants (in dollars per share) | $ / shares	$ 3.00
March 2018 Public Offering | Series 1 Warrant
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]
Number of warrants issued to purchase common stock (in shares)	13,198,075
Exercise price of warrants (in dollars per share) | $ / shares	$ 1.85
March 2018 Public Offering | Series 2 Warrant
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]
Number of warrants issued to purchase common stock (in shares)	7,988,175
Exercise price of warrants (in dollars per share) | $ / shares	$ 2.00