Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
Cash flow from operating activities:
Net loss	$ (139,213)	$ (363,443)
Adjustments to reconcile net loss to net cash used in operating activities
Stock-based compensation	21,838	15,016
Depreciation and amortization	3,106	910
Deferred income taxes	(17,425)	0
Noncash lease expense	883	0
Net accretion and amortization of investments in marketable securities	(519)	(4,495)
Realized gain on sale of available-for-sale marketable securities	(6)	(322)
Change in fair value of warrant liabilities	(189)	(241)
Acquired in-process research and development expense	4,500	249,437
Change in fair value of contingent consideration	6,100	2,700
Changes in operating assets and liabilities:
Accounts receivable	(1,309)	0
Inventory	(1,010)	0
Prepaid expenses and other current assets	(3,321)	(18,056)
Other assets	(1,761)	(5,225)
Accounts payable, accrued and other liabilities	541	20,863
Operating lease liability	(975)	12,172
Deferred revenue	(621)	13,801
Net cash used in operating activities	(129,381)	(76,883)
Cash flow from investing activities:
Cash paid for in-process research and development assets	(4,500)	(175,732)
Purchases of marketable securities	(283,208)	(308,202)
Proceeds from maturities of marketable securities	232,142	364,345
Proceeds from sales of marketable securities	12,987	172,960
Purchases of property and equipment	(657)	(9,584)
Net cash (used in) provided by investing activities	(43,236)	43,787
Cash flow from financing activities:
Payment of contingent consideration	(15,000)	(10,000)
Proceeds from issuance of common stock under equity incentive plans	4,589	8,399
Taxes paid related to net share settlement of equity awards	(2,157)	(658)
Net proceeds from issuance of convertible senior notes	194,000	0
Proceeds from issuance of common stock, net of issuance costs	226,575	0
Net cash provided by (used in) financing activities	408,007	(2,259)
Net increase (decrease) in cash and cash equivalents	235,390	(35,355)
Cash and cash equivalents, beginning of the period	62,070	68,454
Cash and cash equivalents, end of the period	$ 297,460	$ 33,099