Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
Cash flows from operating activities:
Net loss	$ (138,049)	$ (74,858)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	4,367	2,397
Stock-based compensation	21,620	11,043
Amortization of premiums and accretion of discounts on marketable securities	8	(4,027)
Amortization of right-of-use assets	934	1,510
Impairment loss on right-of-use asset	238	1,158
Loss from disposal of property and equipment, net	12	39
Changes in operating assets and liabilities:
Prepaid expenses and other current assets	(3,934)	(1,269)
Other assets	(2,098)	(72)
Accounts payable	1,087	132
Accrued liabilities and accrued clinical supply costs	15,027	7,467
Deferred revenue	(16,245)	(15,218)
Deferred rent		(44)
Lease liabilities	(2,043)	948
Other long-term liabilities		313
Net cash used in operating activities	(119,076)	(70,481)
Cash flows from investing activities:
Purchase of property and equipment	(4,244)	(13,692)
Purchase of marketable securities	(414,949)	(411,239)
Maturities of marketable securities	302,590	346,000
Net cash used in investing activities	(116,603)	(78,931)
Cash flows from financing activities:
Proceeds from issuance of common stock upon initial public offering, net of issuance costs		170,128
Proceeds from issuance of common stock upon follow-on public offering, net of issuance costs	224,603
Proceeds from the exercise of options to purchase common stock	5,699	788
Purchase of common stock under employee stock purchase plan	715
Net cash provided by financing activities	231,017	170,916
Net increase (decrease) in cash, cash equivalents, and restricted cash	(4,662)	21,504
Cash, cash equivalents, and restricted cash at beginning of period	91,113	66,942
Cash, cash equivalents, and restricted cash at end of period	86,451	88,446
Non-cash investing and financing activities:
Property and equipment purchases included in accounts payable and accrued liabilities	$ 337	3,675
Tenant improvements paid by landlord		$ 8,286