CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($)	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Cash flows from operating activities:
Net loss	$ (299,964,000)	$ (266,489,000)	$ (192,256,000)
Adjustments to reconcile net loss to net cash used in operating activities:
Stock-based compensation expense	46,078,000	37,137,000	20,410,000
Depreciation expense	3,014,000	2,305,000	830,000
Noncash lease expense	3,446,000	2,834,000	958,000
Acquired in-process research and development	4,000,000	0	0
Gain on disposal of equipment	0	(7,000)	0
Net accretion of discounts on marketable securities	1,782,000	(1,611,000)	(3,999,000)
Changes in operating assets and liabilities:
Accounts receivable	(6,699,000)	(13,896,000)	0
Inventory	(10,155,000)	(3,241,000)	0
Prepaid expenses and other current assets	(7,934,000)	(1,772,000)	(10,321,000)
Accounts payable	833,000	(7,533,000)	10,862,000
Accrued expenses and other current liabilities	27,285,000	13,923,000	24,189,000
Operating lease liabilities	(2,510,000)	(1,333,000)	(319,000)
Other long-term liabilities	0	0	350,000
Net cash flows used in operating activities	(240,824,000)	(239,683,000)	(149,296,000)
Cash flows from investing activities:
Purchases of marketable securities	(335,375,000)	(1,096,769,000)	(817,142,000)
Maturities of marketable securities	468,587,000	627,913,000	261,216,000
Sales of marketable securities	49,613,000	504,216,000	100,780,000
Purchases of property and equipment	(1,970,000)	(5,316,000)	(4,935,000)
Proceeds from sale of equipment	0	7,000	0
Payments to Acquire in Process Research and Development	(4,000,000)	0	0
Increase in restricted investments	(7,000)	(1,592,000)	(441,000)
Net cash flows provided by (used in) investing activities	176,848,000	28,459,000	(460,522,000)
Cash flows from financing activities:
Proceeds from offerings of common stock, net of underwriting discounts and commissions	8,589,000	207,231,000	432,400,000
Repayment of notes payable to related party	0	0	(1,294,000)
Payments of public offering costs	(40,000)	(815,000)	(620,000)
Proceeds from stock option exercises and employee stock purchase plan	6,341,000	20,385,000	5,888,000
Net cash flows provided by financing activities	14,890,000	226,801,000	436,374,000
Net (decrease) increase in cash and cash equivalents	(49,086,000)	15,577,000	(173,444,000)
Effect of Exchange Rate on Cash and Cash Equivalents	252,000	0	0
Cash and cash equivalents at beginning of period	135,897,000	120,320,000	293,764,000
Cash and cash equivalents at end of period	87,063,000	135,897,000	120,320,000
Supplemental disclosure of cash flow information:
Cash paid for interest	0	0	67,000
Addition of operating lease asset included in accrued expenses and other current liabilities	0	0	562,000
Supplemental disclosure of non-cash investing and financing activities:
Purchases of property and equipment included in accounts payable and accrued expenses and other current liabilities	71,000	239,000	661,000
Unsettled exercise of stock options	$ 0	$ 0	$ 553,000