CONDENSED CONSOLIDATED STATEMENTS OF CHANGES IN STOCKHOLDERS' EQUITY - USD ($) $ in Thousands	Common Stock	Additional Paid-In Capital	Accumulated Other Comprehensive Income	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)	19,890
Stock-based compensation expense		5,262			5,262
Net loss				(49,213)	(49,213)
Balance as of end of period at Jun. 30, 2019	$ 34	311,354		(250,322)	61,066
Balance as of end of period (in shares) at Jun. 30, 2019	33,882,967
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
Balance as of beginning of period at Mar. 31, 2019	$ 34	308,830		(226,497)	82,367
Balance as of beginning of period (in shares) at Mar. 31, 2019	33,882,857
Stockholders' Equity
Exercise of stock options (in shares)	110
Stock-based compensation expense		2,524			2,524
Net loss				(23,825)	(23,825)
Balance as of end of period at Jun. 30, 2019	$ 34	311,354		(250,322)	61,066
Balance as of end of period (in shares) at Jun. 30, 2019	33,882,967
Balance as of beginning of period at Dec. 31, 2019	$ 36	325,112		(295,456)	29,692
Balance as of beginning of period (in shares) at Dec. 31, 2019	36,086,254
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
Balance as of beginning of period at Dec. 31, 2019	$ 36	325,112		(295,456)	29,692
Balance as of beginning of period (in shares) at Dec. 31, 2019	36,086,254
Stockholders' Equity
Common stock offering, net of issuance cost and underwriting fees	$ 17	125,406			125,423
Common stock offering, net of issuance cost and underwriting fees (in shares)	16,979,371
Warrant exercises (in shares)	16,144
At the market offering, net of sales agent commission of $0.4 million	$ 3	12,543			12,546
At the market offering, net of sales agent commission of $0.4 million (in shares)	2,352,671
Exercise of stock options		938			938
Exercise of stock options (in shares)	311,028
Issuance under employee stock purchase plan		270			270
Issuance under employee stock purchase plan (in shares)	85,553
Stock-based compensation expense		5,358			5,358
Net loss				(45,267)	(45,267)
Balance as of end of period at Jun. 30, 2020	$ 56	469,627	$ (17)	(340,723)	128,943
Balance as of end of period (in shares) at Jun. 30, 2020	55,831,021
Balance as of beginning of period at Mar. 31, 2020	$ 55	458,866		(317,411)	141,510
Balance as of beginning of period (in shares) at Mar. 31, 2020	54,585,636
Stockholders' Equity
Common stock offering, net of issuance cost and underwriting fees	$ 1	7,215			7,216
Common stock offering, net of issuance cost and underwriting fees (in shares)	979,371
Warrant exercises (in shares)	16,144
Exercise of stock options		772			772
Exercise of stock options (in shares)	249,870
Stock-based compensation expense		2,774			2,774
Net loss				(23,312)	(23,312)
Balance as of end of period at Jun. 30, 2020	$ 56	$ 469,627	(17)	$ (340,723)	128,943
Balance as of end of period (in shares) at Jun. 30, 2020	55,831,021
Stockholders' Equity
Accumulated other comprehensive income			$ (17)		$ (17)