Quarterly report pursuant to Section 13 or 15(d)

Stockholders' Equity - Outstanding Warrants to Purchase Shares of Common Stock (Detail)

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Stockholders' Equity - Outstanding Warrants to Purchase Shares of Common Stock (Detail)
 3 Months Ended
Mar. 31, 2019
$ / shares
shares
Class Of Warrant Or Right [Line Items]  
Warrants Outstanding, December 31, 2018 3,521,735
Issued 0
Exercised 0
Warrants Outstanding, March 31, 2019 3,521,735
2017 Private Placement Warrants  
Class Of Warrant Or Right [Line Items]  
Warrants Outstanding, December 31, 2018 2,954,462
Issued 0
Exercised 0
Warrants Outstanding, March 31, 2019 2,954,462
Weighted Average Exercise Price | $ / shares $ 6.84
2017 Warrants  
Class Of Warrant Or Right [Line Items]  
Warrants Outstanding, December 31, 2018 377,273
Issued 0
Exercised 0
Warrants Outstanding, March 31, 2019 377,273
Weighted Average Exercise Price | $ / shares $ 39.82
2018 Warrants  
Class Of Warrant Or Right [Line Items]  
Warrants Outstanding, December 31, 2018 190,000
Issued 0
Exercised 0
Warrants Outstanding, March 31, 2019 190,000
Weighted Average Exercise Price | $ / shares $ 9.58