Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($)	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018
Cash flow from operating activities:
Net loss	$ (363,443,000)	$ (101,481,000)
Adjustments to reconcile net loss from continuing operations to net cash used in operating activities:
Stock-based compensation	15,016,000	11,952,000
Depreciation and amortization	910,000	76,000
Net accretion and amortization of investments in marketable securities	(4,495,000)	(521,000)
Realized gain on sale of available-for-sale marketable securities	(322,000)	0
Change in fair value of warrant liabilities	(241,000)	95,000
Acquired in-process research and development and related costs	249,437,000	0
Change in fair value of contingent purchase consideration	2,700,000	3,200,000
Changes in operating assets and liabilities:
Prepaid expenses, escrow holdback and other current assets	(18,056,000)	1,429,000
Other assets	(5,225,000)	551,000
Accounts payable, accrued and other liabilities	20,863,000	1,463,000
Operating lease liability	12,172,000
Deferred revenue	13,801,000	0
Net cash used in operating activities	(76,883,000)	(83,236,000)
Cash flows from investing activities:
Cash paid for asset acquisition, net of cash acquired	(175,732,000)	0
Purchases of marketable securities	(308,202,000)	(375,612,000)
Proceeds from maturities of marketable securities	364,345,000	0
Proceeds from sales of marketable securities	172,960,000	0
Purchases of property and equipment	(9,584,000)	(75,000)
Net cash provided by (used in) investing activities	43,787,000	(375,687,000)
Cash flows from financing activities:
Payment of contingent consideration	(10,000,000)	0
Proceeds from issuance of common stock under equity incentive plans	8,399,000	6,749,000
Taxes paid related to net share settlement of equity awards	(658,000)	(1,426,000)
Proceeds from issuance of common stock, net of issuance costs	0	323,135,000
Net cash (used in) provided by financing activities	(2,259,000)	328,458,000
Net decrease in cash and cash equivalents	(35,355,000)	(130,465,000)
Cash and cash equivalents, beginning of the period	68,454,000	293,503,000
Cash and cash equivalents, end of the period	33,099,000	163,038,000
Noncash investing activities:
Common stock issued as consideration for asset acquisition	68,124,000	0
Net liabilities assumed in connection with asset acquisition	3,688,000	0
Unpaid transaction costs related to asset acquisition	$ 2,449,000	$ 0