CONDENSED CONSOLIDATED STATEMENTS OF STOCKHOLDERS’ EQUITY (DEFICIT) - USD ($) $ in Thousands	Common stock	Additional paid-in capital	Accumulated other comprehensive income (loss)	Accumulated deficit	Total
Balances at Beginning of period (in shares) at Dec. 31, 2018	79,234,853
Balances at Beginning of period at Dec. 31, 2018	$ 79	$ 543,040	$ (29)	$ (150,082)	$ 393,008
Issuance of common stock upon exercise of stock options (in shares)	619,342
Issuance of common stock upon exercise of stock options	$ 1	798			799
Stock-based compensation expense		9,478			9,478
Vesting of restricted common stock		22			22
Unrealized gains on investments			110		110
Net loss				(32,581)	(32,581)
Balances at End of period (in shares) at Mar. 31, 2019	79,854,195
Balances at End of period at Mar. 31, 2019	$ 80	553,338	81	(181,863)	371,636
Balances at Beginning of period (in shares) at Dec. 31, 2018	79,234,853
Balances at Beginning of period at Dec. 31, 2018	$ 79	543,040	(29)	(150,082)	393,008
Net loss					163,500
Balances at End of period (in shares) at Dec. 31, 2019	80,016,245
Balances at End of period at Dec. 31, 2019	$ 80	586,798	75	(312,740)	274,213
Cumulative effect adjustment for adoption of ASC 842				800	800
Issuance of common stock upon exercise of stock options (in shares)	413,721
Issuance of common stock upon exercise of stock options		486			486
Stock-based compensation expense		8,488			8,488
Unrealized gains on investments			456		456
Net loss				(48,486)	(48,486)
Balances at End of period (in shares) at Mar. 31, 2020	80,429,966
Balances at End of period at Mar. 31, 2020	$ 80	$ 595,772	$ 531	$ (361,226)	$ 235,157