Unaudited Consolidated Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Operating activities
Net loss	$ (67,455)	$ (48,939)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation	274	278
Amortization of debt issuance costs and imputed interest	1,714	489
Non-cash interest expense on liability related to sale of future royalty	10,925	0
Stock-based compensation expense	14,679	19,307
Changes in operating assets and liabilities:
Income tax receivable and payable	(22)	(22,218)
Prepaid expenses and other current assets and other assets	1,330	809
Accounts payable	3,629	10,668
Accrued direct research, other current and long-term liabilities	(9,290)	(1,976)
Payable to collaborators	0	1,578
Deferred revenue	(795)	(1,169)
Net cash used in operating activities	(45,011)	(41,173)
Investing activities
Purchases of property and equipment	(193)	(85)
Net cash used in investing activities	(193)	(85)
Financing activities
Exercise of options	4,678	1,422
Net cash provided by financing activities	4,678	1,422
Net decrease in cash and cash equivalents	(40,526)	(39,836)
Cash and cash equivalents at beginning of year	818,150	664,324
Cash and cash equivalents at end of period	777,624	624,488
Supplemental disclosures
Cash paid for interest	0	3,174
Non-cash activity:
Purchases of equipment in accounts payable, accrued direct research, other current, and long-term liabilities	$ 2,523	$ 1,398