Financings - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands					3 Months Ended	12 Months Ended
	Feb. 05, 2020	Sep. 12, 2019	Nov. 11, 2018	May 11, 2017	Sep. 30, 2019	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Apr. 26, 2006
Class of Stock [Line Items]
Stock issued during period				9,708,738		2,814,673
Issuance & sale of common stock in public offering price per share				$ 5.15
Sale of stock price per share				$ 4.893
Sale of stock consideration received on transaction				$ 47,300
Common stock, par value			$ 0.001			$ 0.001	$ 0.001		$ 0.001
Gross proceeds received						$ 6,085	$ 47,101	$ 47,270
Class of warrant or right, number of securities called by warrants or rights			18,939,394
Warrant Exercise Price per share			$ 2.64
Proceeds from private placement		$ 52,500
Non-cash inducement warrant expense					$ (60,751)	$ 60,751
Subsequent Event [Member]
Class of Stock [Line Items]
Stock issued during period	2,814,673
Gross proceeds received	$ 13,000
At The Market Offering [Member]
Class of Stock [Line Items]
Stock issued during period						1,271,274
Sale of stock consideration received on transaction						$ 6,100
At The Market Offering [Member] | Subsequent Event [Member]
Class of Stock [Line Items]
Sale of stock consideration received on transaction	$ 13,000
Private Placement [Member]
Class of Stock [Line Items]
Class of warrant or right, number of securities called by warrants or rights		17,803,031				18,939,394
Warrant Exercise Price per share		$ 3.01				$ 3.01
Placement agent fees and other expenses		$ 1,100
Private Placement [Member] | New Warrants [Member]
Class of Stock [Line Items]
Class of warrant or right, number of securities called by warrants or rights		17,803,031
Warrant Exercise Price per share		$ 7.00
Non-cash inducement warrant expense		$ 60,800				$ 60,800
Securities Purchase Agreement [Member]
Class of Stock [Line Items]
Stock issued during period			18,939,394
Common stock, par value			$ 0.001
par value per share			$ 2.64
Gross proceeds received			$ 47,100			$ 47,100
Underwriting Agreement [Member]
Class of Stock [Line Items]
Stock issued during period						2,814,673
Sale of stock consideration received on transaction						$ 13,000
Underwriting Agreement [Member] | Subsequent Event [Member]
Class of Stock [Line Items]
Stock issued during period	27,826,086
Issuance & sale of common stock in public offering price per share	$ 3.25
Sale of stock consideration received on transaction	$ 85,000
par value per share	$ 3.055
Underwriting Agreement [Member] | Maximum [Member] | Subsequent Event [Member]
Class of Stock [Line Items]
Stock issued during period	4,173,912