Common Stock and Warrants - Warrants Outstanding and Exercisable (Detail)	12 Months Ended
	Dec. 31, 2017 $ / shares shares	Dec. 31, 2017 $ / shares shares
Class Of Warrant Or Right [Line Items]
Number of Warrants Outstanding	2,354,908	2,354,908
Warrants Expiration Date, April 30, 2018
Class Of Warrant Or Right [Line Items]
Number of Warrants Outstanding	90,406	90,406
Exercise Price | $ / shares	$ 15.00
Expiration Date	Apr. 30, 2018
Warrants Expiration Date, June 26, 2018
Class Of Warrant Or Right [Line Items]
Number of Warrants Outstanding	33,546	33,546
Exercise Price | $ / shares	$ 15.00
Expiration Date	Jun. 26, 2018
Warrants Expiration Date, June 26, 2020
Class Of Warrant Or Right [Line Items]
Number of Warrants Outstanding	3,795	3,795
Exercise Price | $ / shares	$ 10.75
Expiration Date	Jun. 26, 2020
Warrants Expiration Date, July 17, 2018
Class Of Warrant Or Right [Line Items]
Number of Warrants Outstanding	12,576	12,576
Exercise Price | $ / shares	$ 15.00
Expiration Date	Jul. 17, 2018
Warrants Expiration Date, July 17, 2020
Class Of Warrant Or Right [Line Items]
Number of Warrants Outstanding	1,509	1,509
Exercise Price | $ / shares	$ 10.75
Expiration Date	Jul. 17, 2020
Warrants Expiration Date, December 29, 2018
Class Of Warrant Or Right [Line Items]
Number of Warrants Outstanding	555,556	555,556
Exercise Price | $ / shares	$ 6.75
Expiration Date	Dec. 29, 2018
Warrants Expiration Date, April 18, 2019
Class Of Warrant Or Right [Line Items]
Number of Warrants Outstanding	961,489	961,489
Exercise Price | $ / shares		$ 7.50
Expiration Date	Apr. 18, 2019
Warrants Expiration Date, April 18, 2018
Class Of Warrant Or Right [Line Items]
Number of Warrants Outstanding	50,015	50,015
Exercise Price | $ / shares		$ 5.00
Expiration Date	Apr. 18, 2018
Warrants Expiration Date, December 22, 2020
Class Of Warrant Or Right [Line Items]
Number of Warrants Outstanding	270,915	270,915
Exercise Price | $ / shares	$ 12.25
Expiration Date	Dec. 22, 2020
Warrants Expiration Date, December 28, 2020
Class Of Warrant Or Right [Line Items]
Number of Warrants Outstanding	171,020	171,020
Exercise Price | $ / shares	$ 12.25
Expiration Date	Dec. 28, 2020
Warrants Expiration Date, December 29, 2020
Class Of Warrant Or Right [Line Items]
Number of Warrants Outstanding	204,081	204,081
Exercise Price | $ / shares	$ 12.25
Expiration Date	Dec. 29, 2020