Condensed Consolidated Statements of Changes in Stockholders' Equity (Deficit) - USD ($)	Total	ATM Offering	2018 Public Offering	2019 Public and Private Offerings	Common Stock	Common Stock ATM Offering	Common Stock 2018 Public Offering	Common Stock 2019 Public and Private Offerings	Additional Paid-In Capital	Additional Paid-In Capital ATM Offering	Additional Paid-In Capital 2018 Public Offering	Additional Paid-In Capital 2019 Public and Private Offerings	Accumulated Other Comprehensive Income (Loss)	Accumulated Deficit
Balance at Dec. 31, 2017	$ (3,059,537)				$ 13,929				$ 131,492,595					$ (134,566,061)
Balance, shares at Dec. 31, 2017					13,929,763
Exercise of stock options	40,504				$ 18				40,486
Exercise of stock options, shares					18,028
Stock-based compensation expense	1,143,188								1,143,188
Release of restricted stock awards	270				$ 270
Release of restricted stock awards, shares					269,551
Net share settlement of restricted stock award	(133,513)				$ (35)				(133,478)
Net share settlement of restricted stock award, shares					(34,769)
Employee stock purchase plan expense	14,453								14,453
Issuance of common stock		$ 556,706	$ 37,724,316			$ 262	$ 13,915			$ 556,444	$ 37,710,401
Issuance of common stock, shares						261,352	13,915,000
Issuance of common stock warrants in connection with MidCapTerm Loan	74,000								74,000
Net loss	(5,379,947)													(5,379,947)
Unrealized gain (loss) on short-term investments	(11,151)												$ (11,151)
Balance at Mar. 31, 2018	30,969,289				$ 28,359				170,898,089				(11,151)	(139,946,008)
Balance, shares at Mar. 31, 2018					28,358,925
Balance at Dec. 31, 2017	$ (3,059,537)				$ 13,929				131,492,595					(134,566,061)
Balance, shares at Dec. 31, 2017					13,929,763
Issuance of common stock, shares	5,733,314				261,352
Balance at Jun. 30, 2018	$ 27,214,616				$ 28,415				171,246,277				(11,339)	(144,048,737)
Balance, shares at Jun. 30, 2018					28,414,524
Balance at Dec. 31, 2017	(3,059,537)				$ 13,929				131,492,595					(134,566,061)
Balance, shares at Dec. 31, 2017					13,929,763
Net loss	(14,326,084)
Unrealized gain (loss) on short-term investments	(8,882)
Balance at Sep. 30, 2018	22,791,326				$ 28,479				171,663,874				(8,882)	(148,892,145)
Balance, shares at Sep. 30, 2018					28,479,341
Balance at Mar. 31, 2018	30,969,289				$ 28,359				170,898,089				(11,151)	(139,946,008)
Balance, shares at Mar. 31, 2018					28,358,925
Exercise of stock options	29,009				$ 16				28,993
Exercise of stock options, shares					15,623
Stock-based compensation expense	241,920								241,920
Stock issued under stock purchase plans	$ 77,315				$ 40				77,275
Stock issued under stock purchase plans, shares					39,976
Issuance of common stock, shares	5,733,314				261,352
Net loss	$ (4,102,729)													(4,102,729)
Unrealized gain (loss) on short-term investments	(188)												(188)
Balance at Jun. 30, 2018	27,214,616				$ 28,415				171,246,277				(11,339)	(144,048,737)
Balance, shares at Jun. 30, 2018					28,414,524
Exercise of stock options	134,660				$ 62				134,598
Exercise of stock options, shares					62,513
Stock-based compensation expense	257,975								257,975
Stock issued under stock purchase plans	25,026				$ 2				25,024
Stock issued under stock purchase plans, shares					2,304
Net loss	(4,843,408)													(4,843,408)
Unrealized gain (loss) on short-term investments	2,457												2,457
Balance at Sep. 30, 2018	22,791,326				$ 28,479				171,663,874				(8,882)	(148,892,145)
Balance, shares at Sep. 30, 2018					28,479,341
Balance at Dec. 31, 2018	21,092,062				$ 28,585				172,086,909				(3,453)	(151,019,979)
Balance, shares at Dec. 31, 2018					28,585,449
Exercise of stock options	51,570				$ 22				51,548
Exercise of stock options, shares					21,871
Stock-based compensation expense	241,233								241,233
Release of restricted stock awards	13				$ 13
Release of restricted stock awards, shares					13,126
Net share settlement of restricted stock award	(9,685)				$ (4)				(9,681)
Net share settlement of restricted stock award, shares					(3,813)
Employee stock purchase plan expense	16,794								16,794
Net loss	(5,370,846)													(5,370,846)
Unrealized gain (loss) on short-term investments	3,353												3,353
Foreign currency translation adjustment	6,439												6,439
Balance at Mar. 31, 2019	16,030,933				$ 28,616				172,386,803				6,339	(156,390,825)
Balance, shares at Mar. 31, 2019					28,616,633
Balance at Dec. 31, 2018	21,092,062				$ 28,585				172,086,909				(3,453)	(151,019,979)
Balance, shares at Dec. 31, 2018					28,585,449
Net loss	(14,908,348)
Unrealized gain (loss) on short-term investments	2,308
Balance at Sep. 30, 2019	28,116,504				$ 58,031				193,953,125				33,675	(165,928,327)
Balance, shares at Sep. 30, 2019					58,031,230
Balance at Mar. 31, 2019	16,030,933				$ 28,616				172,386,803				6,339	(156,390,825)
Balance, shares at Mar. 31, 2019					28,616,633
Exercise of stock options	69,384				$ 32				69,352
Exercise of stock options, shares					32,385
Stock-based compensation expense	287,317								287,317
Release of restricted stock awards	15				$ 15
Release of restricted stock awards, shares					15,001
Net share settlement of restricted stock award	(11,152)				$ (4)				(11,148)
Net share settlement of restricted stock award, shares					(4,461)
Stock issued under stock purchase plans	99,140				$ 48				99,092
Stock issued under stock purchase plans, shares					47,489
Net loss	(4,797,270)													(4,797,270)
Unrealized gain (loss) on short-term investments	819												819
Foreign currency translation adjustment	(9,194)												(9,194)
Balance at Jun. 30, 2019	11,669,992				$ 28,707				172,831,416				(2,036)	(161,188,095)
Balance, shares at Jun. 30, 2019					28,707,047
Stock-based compensation expense	316,525								316,525
Release of restricted stock awards	30				$ 30
Release of restricted stock awards, shares					30,001
Net share settlement of restricted stock award	(7,230)				$ (5)				(7,225)
Net share settlement of restricted stock award, shares					(4,355)
Employee stock purchase plan expense	16,325								16,325
Issuance of common stock and warrants				$ 20,825,383				$ 29,299				$ 20,796,084
Issuance of common stock and warrants, shares								29,298,537
Net loss	(4,740,232)													(4,740,232)
Unrealized gain (loss) on short-term investments	(1,864)												(1,864)
Foreign currency translation adjustment	37,575												37,575
Balance at Sep. 30, 2019	$ 28,116,504				$ 58,031				$ 193,953,125				$ 33,675	$ (165,928,327)
Balance, shares at Sep. 30, 2019					58,031,230