Consolidated Statements of Stockholders' Equity (Unaudited) - USD ($) $ in Thousands	Preferred Stock [Member] Series A Convertible Preferred Shares [Member]	Preferred Stock [Member] Series B Convertible Preferred Shares [Member]	Common Stock [Member]	Treasury Stock [Member]	Additional Paid in Capital [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Accumulated Deficit [Member]	Total
Beginning Balance at Dec. 31, 2017	$ 16,060	$ 25,406	$ 68		$ 5,340	$ 0	$ (31,355)	$ 15,519
Beginning Balance (in shares) at Dec. 31, 2017	128,738	126,909	6,795,627
Conversion of convertible preferred stock into common stock (in shares)	(128,738)	(126,909)
Conversion of convertible preferred stock into common stock	$ (16,060)	$ (25,406)
Conversion of convertible preferred stock into common stock			$ 194		41,272	0	0	0
Conversion of convertible preferred stock into common stock (in shares)			19,475,788
Exchange of common stock in connection with the Merger	$ 0	$ 0	$ 68		85,992	0	0	86,060
Exchange of common stock in connection with the Merger (in shares)	0	0	6,805,608
Issuance of common shares, net of issuance costs	$ 0	$ 0	$ 63		78,455	0	0	78,518
Issuance of common shares, net of issuance costs (in shares)	0	0	6,325,000
Issuance of common stock pursuant to settlement of restricted stock units	$ 0	$ 0	$ 1		(1)	0	0	0
Issuance of common stock pursuant to settlement of restricted stock units (in shares)	0	0	1,875
Unrealized comprehensive gain (loss) on marketable securities/short term investments			$ 0		0	10	0	10
Stock-based compensation			0		5,382	0	0	5,382
Net loss			0		0	0	(15,343)	(15,343)
Ending Balance at Mar. 31, 2018	$ 0	$ 0	$ 394		216,440	10	(46,698)	170,146
Ending Balance (in shares) at Mar. 31, 2018	0	0	39,403,898
Beginning Balance at Dec. 31, 2017	$ 16,060	$ 25,406	$ 68		5,340	0	(31,355)	15,519
Beginning Balance (in shares) at Dec. 31, 2017	128,738	126,909	6,795,627
Unrealized comprehensive gain (loss) on marketable securities/short term investments								(207)
Net loss								(47,199)
Ending Balance at Sep. 30, 2018	$ 0	$ 0	$ 398		221,983	(207)	(78,554)	143,620
Ending Balance (in shares) at Sep. 30, 2018	0	0	39,835,500
Beginning Balance at Mar. 31, 2018	$ 0	$ 0	$ 394		216,440	10	(46,698)	170,146
Beginning Balance (in shares) at Mar. 31, 2018	0	0	39,403,898
Issuance of common stock pursuant to exercise of stock options	$ 0	$ 0	$ 1		(1)	0	0	0
Issuance of common stock pursuant to exercise of stock options (in shares)	0	0	61,536
Issuance of common stock pursuant to settlement of restricted stock units	$ 0	$ 0	$ 0		0	0	0	0
Issuance of common stock pursuant to settlement of restricted stock units (in shares)	0	0	41,093
Unrealized comprehensive gain (loss) on marketable securities/short term investments			$ 0		0	(89)	0	(89)
Stock-based compensation			0		2,786	0	0	2,786
Net loss			0		0	0	(15,767)	(15,767)
Ending Balance at Jun. 30, 2018	$ 0	$ 0	$ 395		219,225	(79)	(62,465)	157,076
Ending Balance (in shares) at Jun. 30, 2018	0	0	39,506,527
Issuance of common stock pursuant to exercise of stock options	$ 0	$ 0	$ 3		146	0	0	149
Issuance of common stock pursuant to exercise of stock options (in shares)	0	0	253,348
Issuance of common stock pursuant to settlement of restricted stock units	$ 0	$ 0	$ 0		0	0	0	0
Issuance of common stock pursuant to settlement of restricted stock units (in shares)	0	0	75,625
Unrealized comprehensive gain (loss) on marketable securities/short term investments			$ 0		0	(128)	0	(128)
Stock-based compensation			0		2,612	0	0	2,612
Net loss			0		0	0	(16,089)	(16,089)
Ending Balance at Sep. 30, 2018	$ 0	$ 0	$ 398		221,983	(207)	(78,554)	143,620
Ending Balance (in shares) at Sep. 30, 2018	0	0	39,835,500
Beginning Balance at Dec. 31, 2018			$ 452	$ (668)	300,253	(127)	(105,873)	194,037
Beginning Balance (in shares) at Dec. 31, 2018			45,194,736
Issuance of common stock pursuant to exercise of stock options			$ 0	0	0	0	0	0
Issuance of common stock pursuant to exercise of stock options (in shares)			19,701
Stock repurchase			$ 0	(725)	(2)	0	0	(727)
Stock repurchase (in shares)			0
Retirement of treasury stock			$ (1)	1,393	(1,392)	0	0	0
Retirement of treasury stock (in shares)			(100,000)
Unrealized comprehensive gain (loss) on marketable securities/short term investments			$ 0	0	0	38	0	38
Stock-based compensation			0	0	3,180	0	0	3,180
Net loss			0	0	0	0	(19,451)	(19,451)
Ending Balance at Mar. 31, 2019			$ 451	0	302,039	(89)	(125,324)	177,077
Ending Balance (in shares) at Mar. 31, 2019			45,114,437
Beginning Balance at Dec. 31, 2018			$ 452	(668)	300,253	(127)	(105,873)	194,037
Beginning Balance (in shares) at Dec. 31, 2018			45,194,736
Unrealized comprehensive gain (loss) on marketable securities/short term investments								244
Net loss								(57,415)
Ending Balance at Sep. 30, 2019			$ 503	(344)	394,930	117	(163,288)	231,918
Ending Balance (in shares) at Sep. 30, 2019			50,376,030
Beginning Balance at Mar. 31, 2019			$ 451	0	302,039	(89)	(125,324)	177,077
Beginning Balance (in shares) at Mar. 31, 2019			45,114,437
Issuance of common stock pursuant to exercise of stock options			$ 0	0	0	0	0	0
Issuance of common stock pursuant to exercise of stock options (in shares)			42,998
Net exercise of options			$ 0	(344)	0	0	0	(344)
Issuance of common shares, net of issuance costs			$ 52		86,028	0	0	86,080
Issuance of common shares, net of issuance costs (in shares)			5,175,000
Unrealized comprehensive gain (loss) on marketable securities/short term investments			$ 0	0	0	233	0	233
Stock-based compensation			0	0	4,138	0	0	4,138
Net loss			0	0	0	0	(18,680)	(18,680)
Ending Balance at Jun. 30, 2019			$ 503	(344)	392,205	144	(144,004)	248,504
Ending Balance (in shares) at Jun. 30, 2019			50,332,435
Issuance of common stock pursuant to exercise of stock options			$ 0	0	31	0	0	31
Issuance of common stock pursuant to exercise of stock options (in shares)			43,595
Unrealized comprehensive gain (loss) on marketable securities/short term investments			$ 0	0	0	(27)	0	(27)
Stock-based compensation			0	0	2,694	0	0	2,694
Net loss			0	0	0	0	(19,284)	(19,284)
Ending Balance at Sep. 30, 2019			$ 503	$ (344)	$ 394,930	$ 117	$ (163,288)	$ 231,918
Ending Balance (in shares) at Sep. 30, 2019			50,376,030