Common Stock - Additional Information (Detail) - USD ($)	1 Months Ended	12 Months Ended
	May 31, 2016	Dec. 31, 2016	Dec. 31, 2015	May 07, 2015	Mar. 31, 2015	Feb. 28, 2015
Class Of Stock [Line Items]
Common stock, shares authorized		200,000,000	200,000,000
Common stock, par value		$ 0.001	$ 0.001
Common stock, sold		75,862,946	58,182,000
Common stock, shares outstanding		75,862,946	58,182,000
Warrants exercise price		$ 0
Warrant liability		$ 9,300,000
Decrease in the fair value of warrant liability		4,800,000
Common stock sales agreement, aggregate offering amount		$ 76,000	$ 58,000
Offering, issuance and sale of stocks and securities, shelf registration					$ 250,000,000
Sale of stock		0
Maximum
Class Of Stock [Line Items]
Offering, issuance and sale of stocks and securities, shelf registration				$ 100,000,000
F B R Co
Class Of Stock [Line Items]
Common stock, sold		5,900,000
proceeds from sale of shares		$ 10,200,000
Common stock available for sale under Sales Agreement		$ 9,100,000
F B R Co | Maximum
Class Of Stock [Line Items]
Common stock sales agreement, aggregate offering amount				$ 15,000,000		$ 17,900,000
Common stock sales agreement commission, percentage						3.00%
PIPE Warrants [Member] | Private Placement
Class Of Stock [Line Items]
Common stock, sold	17,642,482
Shares issued, price per share	$ 0.965
Gross proceeds from issuance of private placement	$ 17,000,000
Exchange of unit to share	1
Warrants exercise price	$ 1.00
Warrants exercisable period	5 years
Director and Executive Officer | PIPE Warrants [Member] | Private Placement
Class Of Stock [Line Items]
Common stock, sold	544,039
Net offering proceeds to the company	$ 15,400,000