Consolidated Statements of Changes in Stockholders' Equity - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-in Capital	Accumulated Deficit	Accumulated Other Comprehensive Income (Loss)
Balances at Dec. 31, 2016	$ 62,966	$ 1	$ 108,246	$ (45,277)	$ (4)
Balances (in shares) at Dec. 31, 2016		13,431,000
Issuance of common stock in connection with employee stock purchase plan	131		131
Issuance of common stock in connection with employee stock purchase plan (in shares)		39,000
Issuance of common stock in connection with exercise of stock options	702		702
Issuance of common stock in connection with exercise of stock options (in shares)		200,000
Issuance of common stock in connection with initial public offering/ follow-on offering/ at-the-market offerings, net of offering costs	11,380	$ 1	11,379
Issuance of common stock in connection with initial public offering/ follow-on offering at-the-market offerings, net of offering costs (in shares)		3,000,000
Stock-based compensation expense	2,492		2,492
Unrealized gain (loss) on marketable securities	(98)				(98)
Net loss	(27,236)			(27,236)
Balances at Dec. 31, 2017	50,337	$ 2	122,950	(72,513)	(102)
Balances (in shares) at Dec. 31, 2017		16,670,000
Issuance of common stock in connection with employee stock purchase plan	207		207
Issuance of common stock in connection with employee stock purchase plan (in shares)		56,000
Issuance of common stock in connection with exercise of stock options	2,829		2,829
Issuance of common stock in connection with exercise of stock options (in shares)		521,000
Issuance of common stock in connection with initial public offering/ follow-on offering/ at-the-market offerings, net of offering costs	54,048		54,048
Issuance of common stock in connection with initial public offering/ follow-on offering at-the-market offerings, net of offering costs (in shares)		6,893,000
Stock-based compensation expense	4,280		4,280
Unrealized gain (loss) on marketable securities	75				75
Net loss	(44,348)			(44,348)
Balances at Dec. 31, 2018	67,428	$ 2	184,314	(116,861)	(27)
Balances (in shares) at Dec. 31, 2018		24,140,000
Issuance of common stock in connection with employee stock purchase plan	307		307
Issuance of common stock in connection with employee stock purchase plan (in shares)		45,000
Issuance of common stock in connection with exercise of stock options	$ 1,143		1,143
Issuance of common stock in connection with exercise of stock options (in shares)	274,436	274,000
Issuance of common stock and pre-funded warrants in connection with public offering, net of offering costs	$ 64,503	$ 1	64,502
Issuance of common stock and pre-funded warrants in connection with public offering, net of offering costs (in shares)		4,625,000
Stock-based compensation expense	4,876		4,876
Unrealized gain (loss) on marketable securities	78				78
Net loss	(78,254)			(78,254)
Balances at Dec. 31, 2019	$ 60,081	$ 3	$ 255,142	$ (195,115)	$ 51
Balances (in shares) at Dec. 31, 2019		29,084,000