Condensed Consolidated Statements of Changes in Stockholders' Equity (Deficit) - USD ($)	Total	ATM Offering	Underwritten Public Offering	Common Stock	Common Stock ATM Offering	Common Stock Underwritten Public Offering	Additional Paid-In Capital	Additional Paid-In Capital ATM Offering	Additional Paid-In Capital Underwritten Public Offering	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		$ 261	$ 13,915		$ 556,445	$ 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			$ 28,358			170,898,090			(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
Net loss	$ (9,482,676)
Unrealized gain (loss) on short-term investments	(11,339)
Balance at Jun. 30, 2018	27,214,616			$ 28,414			171,246,278			(11,339)	(144,048,737)
Balance, shares at Jun. 30, 2018				28,414,524
Balance at Mar. 31, 2018	30,969,289			$ 28,358			170,898,090			(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			$ 28,414			171,246,278			(11,339)	(144,048,737)
Balance, shares at Jun. 30, 2018				28,414,524
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	(10,168,116)
Unrealized gain (loss) on short-term investments	4,172
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
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