Common and Preferred Stock - Additional Information (Detail) - USD ($)			1 Months Ended				12 Months Ended
	Dec. 26, 2019	Dec. 23, 2019	Jul. 31, 2019	Dec. 31, 2018	Apr. 30, 2018	Feb. 28, 2018	Dec. 31, 2019	Dec. 31, 2018
Class of Stock [Line Items]
Common stock, shares authorized				280,000,000			280,000,000	280,000,000
Common stock, par value				$ 0.01			$ 0.01	$ 0.01
Undesignated preferred stock, shares authorized				10,000,000			10,000,000	10,000,000
Undesignated preferred stock, par value				$ 0.01			$ 0.01	$ 0.01
Common stock, shares issued				187,029,967			211,787,573	187,029,967
Common stock, shares outstanding				187,029,967			211,787,573	187,029,967
Undesignated preferred stock, shares outstanding				0			0	0
Other expense							$ (7,306,000)	$ (10,140,000)
Common Stock | Public Offering
Class of Stock [Line Items]
Number of shares sold during the period								26,667,000
Purchase Agreements
Class of Stock [Line Items]
Stock purchase agreements date					Apr. 30, 2018	Feb. 28, 2018
Purchase Agreements | Common Stock
Class of Stock [Line Items]
Amount of net proceeds from issuance of securities					$ 26,400,000
Number of shares sold during the period					14,000,000
Exchange price per share					$ 2.00
Purchase Agreements | Warrants
Class of Stock [Line Items]
Exercise price of warrants					$ 2.38
Warrants expiration, date					Apr. 09, 2019
Closing of Offering Date					Apr. 09, 2018
Purchase Agreements | Warrants | Maximum
Class of Stock [Line Items]
Warrants to purchase common stock					14,000,000
Contolled Equity Offering Sales Agreement | Cantor Fitzgerald | Common Stock | Maximum
Class of Stock [Line Items]
Amount of net proceeds from issuance of securities						$ 50,000,000
At Market Issuance Sales Agreement
Class of Stock [Line Items]
Amount of net proceeds from issuance of securities							$ 0	$ 400,000
Number of shares sold during the period							0	230,445
At Market Issuance Sales Agreement | Cantor Fitzgerald | Common Stock
Class of Stock [Line Items]
Amount of net proceeds from issuance of securities							$ 3,200,000	$ 2,100,000
Number of shares sold during the period							2,584,964	1,028,432
Exchange price per share				$ 2.03			$ 1.24	$ 2.03
Underwriting Agreement with Leerink Partners LLC
Class of Stock [Line Items]
Stock purchase agreements date				Dec. 31, 2018
Exercise price of warrants		$ 1.311
Warrants expiration, date		Jun. 26, 2020		Dec. 26, 2019
Warrants modified		11,750,000
Warrants exercised		4,500,000
Warrants expired unexercised	11,583,333
Remaining warrants available for purchase							7,250,000
Underwriting Agreement with Leerink Partners LLC | Minimum
Class of Stock [Line Items]
Warrants exercised		4,500,000
Underwriting Agreement with Leerink Partners LLC | Common Stock
Class of Stock [Line Items]
Amount of net proceeds from issuance of securities				$ 37,300,000
Exchange price per share				$ 1.50				1.50
Underwriting Agreement with Leerink Partners LLC | Common Stock | Public Offering
Class of Stock [Line Items]
Number of shares sold during the period				26,666,667
Underwriting Agreement with Leerink Partners LLC | Warrants
Class of Stock [Line Items]
Amount of net proceeds from issuance of securities		$ 5,900,000
Exercise price of warrants				$ 1.60			$ 1.60	$ 1.60
Closing of Offering Date							Jun. 26, 2020
Repurchase of common stock , shares			3,333,334
Repurchase of common stock , value			$ 400,000
Additional paid-in capital		$ 700,000	200,000
Other expense			$ 200,000
Underwriting Agreement with Leerink Partners LLC | Warrants | Maximum
Class of Stock [Line Items]
Warrants to purchase common stock				26,666,667				26,666,667