Stockholders' Equity - Additional Information (Detail) - shares	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Nov. 30, 2013
Equity [Abstract]
Shares of common stock, authorized (in shares)	600,000,000
Shares of common stock, issued and sold (in shares)	184,739,169
Stock issued during period, shares, new issues (in shares)	1,882,821	2,287,099
2018 Warrants
Class of Stock [Line Items]
Number of shares to be issued upon exercise of the 2018 Warrants	2,700,000		7,783,023