Condensed Consolidated Statements of Redeemable Convertible Preferred Stock and Stockholders' Equity (Deficit) - USD ($) $ in Thousands	Total	Series A Redeemable Convertible Preferred Stock	Series B Redeemable Convertible Preferred Stock	Common Stock	Additional Pain In Capital	Accumulated Deficit	Accumulated Other Comprehensive Income (Loss)
Balance at Dec. 31, 2017	$ (31,929)			$ 1	$ 1,849	$ (33,779)
Balance, shares at Dec. 31, 2017				4,562,640
Balance, temporary equity, shares at Dec. 31, 2017		15,527,951	4,792,716
Balance, temporary equity at Dec. 31, 2017		$ 41,674	$ 39,946
Conversion of convertible preferred stock into common stock upon the closing of initial public offering, Shares		(15,527,951)	(4,792,716)	15,870,559
Conversion of convertible preferred stock into common stock upon the closing of initial public offering	81,620	$ (41,674)	$ (39,946)	$ 1	81,619
Issuance of common stock	89,370			$ 1	89,369
Issuance of common stock, Shares				6,516,667
Vesting of restricted shares, value	865				865
Vesting of restricted shares				1,096,449
Stock-based compensation expense	316				316
Net loss	(9,859)					(9,859)
Balance at Mar. 31, 2018	130,383			$ 3	174,018	(43,638)
Balance, shares at Mar. 31, 2018				28,046,315
Balance, temporary equity, shares at Mar. 31, 2018		0	0
Balance, temporary equity at Mar. 31, 2018		$ 0	$ 0
Balance at Dec. 31, 2018	$ 104,204			$ 3	175,635	(71,393)	$ (41)
Balance, shares at Dec. 31, 2018	28,054,344			28,054,344
Issuance of common stock	$ 46,585			$ 1	46,584
Issuance of common stock, Shares				7,200,000
Vesting of restricted shares, value	1				1
Vesting of restricted shares				500
Stock-based compensation expense	662				662
Net loss	(11,069)					(11,069)
Unrealized gain (losses) on marketable securities	73						73
Balance at Mar. 31, 2019	$ 140,456			$ 4	$ 222,882	$ (82,462)	$ 32
Balance, shares at Mar. 31, 2019	35,254,844			35,254,844