Equity Financing - Additional Information (Detail) - USD ($)		1 Months Ended				12 Months Ended
	Jul. 23, 2015	Oct. 31, 2017	Jan. 31, 2017	Sep. 30, 2016	Aug. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Apr. 30, 2017
2017 Placement Warrants
Subsidiary Sale Of Stock [Line Items]
Warrants to purchase common stock, shares			1,720,512
Warrant exercise price			$ 3.17
Warrant exercisable date			Jul. 31, 2017
Warrant expiration date			Jan. 31, 2024
2016 Placement Warrants Liability
Subsidiary Sale Of Stock [Line Items]
Warrants to purchase common stock, shares				1,380,745	1,380,745
Warrant exercise price				$ 2.95	$ 2.95
Warrant expiration period				7 years	7 years
Private Placement
Subsidiary Sale Of Stock [Line Items]
Private placement, common shares	5,884,504
Proceed from private placement and equity issuances, gross			$ 26,100,000	$ 13,800,000		$ 26,100,000	$ 13,800,000
Private Placement | Common Stock
Subsidiary Sale Of Stock [Line Items]
Private placement, common shares			8,602,589	4,602,506
Stock issued during period						8,602,589	4,602,506	5,884,504
At The Market Offering Program
Subsidiary Sale Of Stock [Line Items]
Proceeds from offering of common stock, gross						$ 40,126,000	$ 0	$ 0
Compensation percentage pertaining to gross sales price per share sold						3.00%
Stock issued during period						0
Average market price per share						$ 6.10
At The Market Offering Program | Maximum
Subsidiary Sale Of Stock [Line Items]
Maximum aggregate offering price			$ 75,000,000						$ 100,000,000
Maximum common stock saleable value			$ 25,000,000						$ 25,000,000
At The Market Offering Program | Common Stock
Subsidiary Sale Of Stock [Line Items]
Stock issued during period						6,575,062
2017 Direct Registered Offering
Subsidiary Sale Of Stock [Line Items]
Proceeds from offering of common stock, gross		$ 50,000,000
2017 Direct Registered Offering | Common Stock
Subsidiary Sale Of Stock [Line Items]
Private placement, common shares		8,382,643