Consolidated Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019
Cash flows from operating activities:
Net loss	$ (67,241)	$ (21,460)	$ (140,048)	$ (68,844)	$ (192,300)
Adjustments to reconcile net loss to net cash flows used in operating activities:
Stock-based compensation expense			17,603	10,336
Depreciation expense			944	216
Noncash lease expense			1,062	337
Net accretion of discounts on marketable securities			(2,010)	(1,297)
Changes in operating assets and liabilities:
Accounts Receivable			(7,384)	(20,000)
Unbilled Receivables			0	(5,000)
Inventory			(798)	0
Prepaid expenses and other current assets			(146)	1,263
Accounts payable			(7,056)	5,592
Accrued expenses and other current liabilities			(2,436)	7,239
Operating lease liabilities			(945)	(349)
Other long-term liabilities			0	235
Net cash flows used in operating activities			(141,214)	(70,272)
Cash flows from investing activities:
Purchases of marketable securities			(818,182)	(253,759)
Maturities of marketable securities			323,263	68,364
Sales of marketable securities			479,746	18,688
Purchases of property and equipment			(3,653)	(244)
Increase in restricted investments			(615)	(441)
Net cash flows used in investing activities			(19,441)	(167,392)
Cash flows from financing activities:
Proceeds from public offerings, net of underwriting discounts and commissions			189,037	0
Repayment of notes payable to related party			0	(93)
Payments of public offering costs			(652)	0
Proceeds from exercise of stock options			7,396	1,230
Net cash flows provided by financing activities			195,781	1,137
Net increase (decrease) in cash and cash equivalents			35,126	(236,527)
Cash and cash equivalents at beginning of period			120,320	293,764	293,764
Cash and cash equivalents at end of period	$ 155,446	$ 57,237	155,446	57,237	$ 120,320
Supplemental disclosure of cash flow information:
Cash paid for interest			0	38
Inventory purchases included in accrued expenses and other current liabilities			591	0
Property and equipment purchases included in accounts payable and accrued expenses and other current liabilities			$ 525	$ 0