CONSOLIDATED STATEMENTS OF STOCKHOLDERS’ EQUITY - USD ($) $ in Thousands	Common Stock	Additional Paid-In Capital	Accumulated Deficit	Total
Balance as of beginning of period at Dec. 31, 2018	$ 34	$ 306,053	$ (201,109)	$ 104,978
Balance as of beginning of period (in shares) at Dec. 31, 2018	33,863,077
Stockholders' Equity
Exercise of stock options		39		39
Exercise of stock options (in shares)	19,780
Stock-based compensation expense		2,738		2,738
Net loss			(25,388)	(25,388)
Balance as of end of period at Mar. 31, 2019	$ 34	308,830	(226,497)	82,367
Balance as of end of period (in shares) at Mar. 31, 2019	33,882,857
Balance as of beginning of period at Dec. 31, 2018	$ 34	306,053	(201,109)	104,978
Balance as of beginning of period (in shares) at Dec. 31, 2018	33,863,077
Balance as of end of period at Dec. 31, 2019	$ 36	325,112	(295,456)	29,692
Balance as of end of period (in shares) at Dec. 31, 2019	36,086,254
Stockholders' Equity
Common stock offering, net of issuance cost and underwriting fees of $8.1 millio	$ 16	118,191		118,207
Common stock offering, net of issuance cost and underwriting fees (in shares)	16,000,000
At-the-market offering, net of sales agent commission and fees	$ 3	12,543		12,546
At-the-market offering, net of sales agent commission and fees (in shares)	2,352,671
Exercise of stock options		167		167
Exercise of stock options (in shares)	61,158
Issuance under employee stock purchase plan		269		269
Issuance under employee stock purchase plan (in shares)	85,553
Stock-based compensation expense		2,584		2,584
Net loss			(21,955)	(21,955)
Balance as of end of period at Mar. 31, 2020	$ 55	$ 458,866	$ (317,411)	$ 141,510
Balance as of end of period (in shares) at Mar. 31, 2020	54,585,636