Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Operating activities
Net loss	$ (50,532)	$ (21,310)
Reconciliation of net loss to net cash used in operating activities:
Stock-based compensation	5,285	2,573
Depreciation and amortization	90	73
Amortization of operating lease right-of-use assets	95	83
Non-cash interest expense related to the revenue interest liability	3,381	0
Net amortization (accretion) on investments	6	(52)
Change in fair value of derivative liability	(334)	0
Change in operating assets and liabilities:
Prepaid and other current assets	(112)	(158)
Other assets	(160)	0
Accounts payable, accrued expenses and other liabilities	17,228	476
Operating lease liabilities	(157)	(36)
Net cash used in operating activities	(25,210)	(18,351)
Investing activities
Proceeds from maturities of investments	48,600	29,500
Proceeds from paydown of investments	2,000	4,359
Purchase of investments	(83,381)	0
Purchase of property and equipment	(3)	(98)
Net cash (used in) provided by investing activities	(32,784)	33,761
Financing activities
Proceeds from issuance of common stock in public offerings, net of issuance costs	6,914	44,659
Proceeds from issuance of common stock pursuant to equity award plans	80	0
Payment of issuance costs related to the revenue interest liability	(400)	0
Net cash provided by financing activities	6,594	44,659
Effect of exchange rate on cash and cash equivalents	(9)	(4)
Net (decrease) increase in cash and cash equivalents	(51,409)	60,065
Cash and cash equivalents at beginning of period	142,086	11,970
Cash and cash equivalents at end of period	90,677	72,035
Supplemental disclosure of cash flow information:
Operating cash flows paid for operating lease	$ 212	$ 107