Common and Preferred Stock - Additional Information (Detail) $ / shares in Units, $ in Thousands							3 Months Ended	12 Months Ended
	Dec. 19, 2018 USD ($) $ / shares shares	Apr. 05, 2018 USD ($) $ / shares shares	Feb. 28, 2018 USD ($)	Oct. 23, 2017 shares	Oct. 10, 2017 USD ($) $ / shares shares	Mar. 01, 2017	Dec. 31, 2017 USD ($) $ / shares shares	Dec. 31, 2018 USD ($) $ / shares shares	Dec. 31, 2016 USD ($)	Dec. 13, 2017 $ / shares shares	Dec. 12, 2017 shares
Class of Stock [Line Items]
Reverse stock split, description								On March 1, 2017, the Company effected a 1-for-5 reverse stock split of the Company’s outstanding common stock. As a result, prior to March 1, 2017, all common stock share amounts included in these consolidated financial statements have been retroactively reduced by a factor of five, and all common stock per share amounts have been increased by a factor of five, with the exception of the Company’s common stock par value.
Common stock, shares authorized							280,000,000	280,000,000		280,000,000	140,000,000
Common stock, par value | $ / shares							$ 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 | $ / shares							$ 0.01	$ 0.01		$ 0.01
Common stock, shares issued							119,053,414	187,029,967
Common stock, shares outstanding							119,053,414	187,029,967
Undesignated preferred stock, shares outstanding							0	0
Amount of net proceeds from issuance of securities | $									$ 893
At Market Issuance Sales Agreement
Class of Stock [Line Items]
Number of shares sold during the period								230,445
Amount of net proceeds from issuance of securities | $								$ 400
Purchase Agreements
Class of Stock [Line Items]
Stock purchase agreements date		Apr. 05, 2018	Feb. 28, 2018		Oct. 10, 2017
Placement agent fees					5.00%
Common Stock
Class of Stock [Line Items]
Stock split of common stock						0.2
Number of shares sold during the period				973,236
Common Stock | Public Offering
Class of Stock [Line Items]
Number of shares sold during the period								26,667,000
Common Stock | Underwriting Agreement with Leerink Partners LLC
Class of Stock [Line Items]
Exchange price per share | $ / shares	$ 1.50
Amount of net proceeds from issuance of securities | $	$ 37,300
Closing of Offering Date	Dec. 26, 2018
Common Stock | Underwriting Agreement with Leerink Partners LLC | Public Offering
Class of Stock [Line Items]
Number of shares sold during the period	26,666,667
Common Stock | Purchase Agreements
Class of Stock [Line Items]
Number of shares sold during the period		14,000,000			10,166,600
Exchange price per share | $ / shares		$ 2.00			$ 6.00
Amount of net proceeds from issuance of securities | $		$ 26,400			$ 57,700
Common Stock | Charitable Foundation | Chairman of Board of Directors
Class of Stock [Line Items]
Number of shares sold during the period					166,600
Common Stock | FBR Capital Markets & Co. | At Market Issuance Sales Agreement
Class of Stock [Line Items]
Number of shares sold during the period							173,327
Exchange price per share | $ / shares							$ 3.15
Amount of net proceeds from issuance of securities | $							$ 500
Common Stock | Cantor Fitzgerald | At Market Issuance Sales Agreement
Class of Stock [Line Items]
Number of shares sold during the period								1,028,432
Exchange price per share | $ / shares								$ 2.03
Amount of net proceeds from issuance of securities | $								$ 2,100
Common Stock | Cantor Fitzgerald | Contolled Equity Offering Sales Agreement | Maximum
Class of Stock [Line Items]
Amount of net proceeds from issuance of securities | $			$ 50,000
Warrants | Underwriting Agreement with Leerink Partners LLC
Class of Stock [Line Items]
Exercise price of warrants | $ / shares	$ 1.60
Warrants expiration, date	Dec. 26, 2019
Warrants | Underwriting Agreement with Leerink Partners LLC | Maximum
Class of Stock [Line Items]
Warrants to purchase common stock	26,666,667
Warrants | Purchase Agreements
Class of Stock [Line Items]
Exercise price of warrants | $ / shares		$ 2.38
Warrants expiration, date		Apr. 09, 2019
Closing of Offering Date		Apr. 09, 2018
Warrants | Purchase Agreements | Maximum
Class of Stock [Line Items]
Warrants to purchase common stock		14,000,000