Liquidity and Going Concern Uncertainty- Additional Information (Detail) - USD ($)										1 Months Ended	3 Months Ended		12 Months Ended
	Mar. 19, 2019	Mar. 11, 2019	Feb. 12, 2019	Jan. 18, 2019	Sep. 20, 2018	Aug. 13, 2018	May 24, 2018	Jan. 31, 2018	Jan. 30, 2018	Feb. 29, 2016	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018	May 31, 2018	Dec. 31, 2017
Liquidity And Managements Plans [Line Items]
Cash											$ 14,762,198	$ 9,272,420	$ 3,423,373		$ 2,146,611
Accumulated deficit											(226,474,108)		(220,457,578)
Net loss											(5,916,787)	(6,356,404)	$ (24,600,000)
Aggregate net interest-bearing indebtedness											1,600,000
Aggregate net interest-bearing indebtedness due within one year											640,000
Other non-interest bearing current liabilities											4,400,000
Unconditional purchase commitment aggregate amount										$ 1,062,500	$ 278,000
Unconditional purchase commitment payment terms											Quarterly
Unconditional purchase commitment period											May 31, 2020
Proceeds from issuance of common stock, net of issuance costs	$ 7,500,000			$ 2,000,000
Proceeds from exercise of common stock warrants											$ 4,748	$ 0
Stock price	$ 1.37			$ 2.25	$ 3.285
Exercise price of unregistered warrants	$ 1.25		$ 1.20			$ 4.53			$ 1.20
Aggregate units sold under right offering						11,587
Shares issued in offering	5,950,000			990,000
Warrant exercisable for share of common stock	1					1
Net proceeds from issuance of units, net of issuance expenses					$ 2,200,000	$ 10,100,000
Public offering, number of common stock and warrants issued					642,438
Class of warrant or rights, term	5 years 6 months								5 years
Prefunded Warrants [Member]
Liquidity And Managements Plans [Line Items]
Exercise price of unregistered warrants					$ 3.275
Change in exercise price of warrants					0.01
Warrant [Member]
Liquidity And Managements Plans [Line Items]
Aggregate warrants sold under right offering						2,549,140
Series A Preferred Stock [Member]
Liquidity And Managements Plans [Line Items]
Shares issued in offering						11,587
Follow-on Public Offering [Member]
Liquidity And Managements Plans [Line Items]
Proceeds from issuance of common stock, net of issuance costs		$ 592,000	$ 6,600,000						$ 13,300,000
Proceeds from exercise of common stock warrants			$ 0					$ 0	0
Proceeds from gross exercise of common stock warrants outstanding									$ 1,300,000
Exercisable warrant available price per share									$ 1.20
Exercisable warrant available price per share expiration period									2023-01
Private offering, number of common stock and warrants issued									1,095,153
Stock price		$ 1.20	$ 1.20						$ 13.50
Exercise price of unregistered warrants	$ 1.25		$ 1.20						$ 1.20
Shares issued in offering			6,250,000
Public offering, number of common stock and warrants issued									1,095,153
Class of warrant or rights, term	5 years 6 months		5 years						5 years
Purchase of common stock by underwriters to cover overallotments, number of shares		538,867
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 unregistered warrants					$ 3.16
Warrant exercisable for share of common stock					1
Class of warrant or rights, term					5 years
Over-allotment Option [Member] | Warrant [Member]
Liquidity And Managements Plans [Line Items]
Shares issued in offering			915,000
Minimum [Member]
Liquidity And Managements Plans [Line Items]
Unconditional purchase commitment, quarterly payment amount										$ 62,500
Maximum [Member] | Prefunded Warrants [Member]
Liquidity And Managements Plans [Line Items]
Issuance of warrants to purchase shares of common stock					120,000
Maximum [Member] | Follow-on Public Offering [Member]
Liquidity And Managements Plans [Line Items]
Issuance of warrants to purchase shares of common stock			6,250,000						1,095,153
Maximum [Member] | Shelf Registration Statement [Member]
Liquidity And Managements Plans [Line Items]
Aggregate offering price							$ 50,000,000							$ 50,000,000
Maximum [Member] | Over-allotment Option [Member]
Liquidity And Managements Plans [Line Items]
Issuance of warrants to purchase shares of common stock			937,500