Liquidity and Going Concern Uncertainty- Additional Information (Detail) - USD ($)						1 Months Ended			3 Months Ended		9 Months Ended
	Sep. 20, 2018	Aug. 13, 2018	Jan. 31, 2018	Jan. 30, 2018	Aug. 09, 2017	May 31, 2018	Feb. 29, 2016	May 31, 2015	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017	Mar. 31, 2017	Dec. 31, 2016
Liquidity And Managements Plans [Line Items]
Cash									$ 8,956,200	$ 5,879,025	$ 8,956,200	$ 5,879,025	$ 2,146,611		$ 4,609,332
Accumulated deficit									(214,444,005)		(214,444,005)		$ (195,249,607)
Net loss									(6,047,784)	(5,821,306)	(18,558,028)	(15,947,164)
Unconditional purchase commitment aggregate amount							$ 1,062,500		404,000		$ 404,000
Unconditional purchase commitment payment terms											Quarterly
Unconditional purchase commitment period											May 31, 2020
Shelf registration statement expiration period								May 21, 2018
Public offering, number of common stock and warrants issued	642,438			1,095,153
Stock price	$ 3.285			$ 13.50
Exercise price of warrants		$ 4.53		$ 4.53										$ 75.00
Net proceeds from issuance of units, net of issuance expenses	$ 2,200,000	$ 10,200,000
Warrant exercisable for share of common stock		1
Class of warrant or rights, term		5 years		5 years
Aggregate units sold under right offering		11,587
Shares issued in offering	642,438
Proceeds from issuance of common stock, net of issuance costs	$ 2,200,000
Proceeds from exercise of common stock warrants		$ 0									$ 0	7,498,535
Proceeds from issuance of common stock	$ 2,500,000	$ 11,600,000
Ally Bridge [Member]
Liquidity And Managements Plans [Line Items]
Issuance of warrants to purchase shares of common stock					47,821
Stock price					$ 45.00
Exercise price of warrants					$ 45.00
Class of warrant or rights, term					5 years
Proceeds from issuance of common stock, net of issuance costs					$ 2,000,000
Proceeds from exercise of common stock warrants					$ 0
Exercisable warrant available price per share expiration period					2022-08
Proceeds from issuance of common stock					$ 2,200,000
Prefunded Warrants [Member]
Liquidity And Managements Plans [Line Items]
Issuance of warrants to purchase shares of common stock	120,000
Exercise price of warrants	$ 3.275
Change in exercise price of warrants	0.01
Series A Preferred Stock [Member]
Liquidity And Managements Plans [Line Items]
Shares issued in offering		11,587
Warrants [Member]
Liquidity And Managements Plans [Line Items]
Aggregate warrants sold under right offering		2,549,140
Shelf Registration Statement [Member]
Liquidity And Managements Plans [Line Items]
Shelf registration statement expiration period						May 31, 2021
Minimum public float limit for offering						$ 75,000,000		$ 75,000,000
Private Placement [Member]
Liquidity And Managements Plans [Line Items]
Exercise price of warrants	$ 3.16
Warrant exercisable for share of common stock	1
Class of warrant or rights, term	5 years
Follow-on Public Offering [Member]
Liquidity And Managements Plans [Line Items]
Public offering, number of common stock and warrants issued				1,095,153
Stock price				$ 13.50
Exercise price of warrants	$ 3.16	$ 4.53		$ 4.53
Class of warrant or rights, term	5 years	5 years		5 years
Proceeds from issuance of common stock, net of issuance costs				$ 13,300,000
Proceeds from exercise of common stock warrants			$ 0	0
Proceeds from gross exercise of common stock warrants outstanding				$ 16,400,000
Exercisable warrant available price per share				$ 4.53
Exercisable warrant available price per share expiration period				2023-01
April 2014 Credit Facility [Member]
Liquidity And Managements Plans [Line Items]
Aggregate net interest-bearing indebtedness									1,700,000	3,300,000	1,700,000	3,300,000
Aggregate net interest-bearing indebtedness due within one year									$ 693,000	$ 2,400,000	$ 693,000	$ 2,400,000
Minimum [Member]
Liquidity And Managements Plans [Line Items]
Unconditional purchase commitment, quarterly payment amount							$ 62,500
Maximum [Member]
Liquidity And Managements Plans [Line Items]
Issuance of warrants to purchase shares of common stock				1,095,153
Maximum [Member] | Prefunded Warrants [Member]
Liquidity And Managements Plans [Line Items]
Issuance of warrants to purchase shares of common stock	120,000
Maximum [Member] | Shelf Registration Statement [Member]
Liquidity And Managements Plans [Line Items]
Aggregate offering price						$ 50,000,000		$ 50,000,000
Maximum [Member] | Follow-on Public Offering [Member]
Liquidity And Managements Plans [Line Items]
Issuance of warrants to purchase shares of common stock				1,095,153