Consolidated Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended				12 Months Ended
	Dec. 31, 2019	Mar. 31, 2019	Dec. 31, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Operating activities:
Net loss	$ (56,060)	$ (35,202)	$ (22,433)	$ (30,180)	$ (419,503)	$ (123,914)	$ (126,817)
Adjustments to reconcile net loss to net cash used in operating activities:
Stock-based compensation					21,247	15,492	6,155
Depreciation					1,268	155	425
Amortization of debt issuance costs and debt discount					0	0	887
Net accretion and amortization of investments in marketable securities					(4,887)	(1,998)	0
Realized gain on sale of marketable securities					(326)	0	0
Change in fair value of common stock warrant liabilities					(145)	(169)	(297)
Acquired in-process research and development assets and related costs						251,437	0	$ 0
Change in fair value of contingent consideration					5,600	1,300	24,100
Inventory write-down					0	0	2,232
Asset impairment charges					0	0	1,116
Loss on extinguishment of debt					0	0	4,876
Changes in operating assets and liabilities:
Trade accounts receivable					0	0	9,356
Inventory					0	0	2,583
Prepaid expenses and other current assets					7,573	(9,335)	(801)
Other assets					(4,502)	266	(2,784)
Accounts payable, accrued and other liabilities					5,647	6,545	4,340
Operating lease liability					11,720
Deferred revenue					13,352	0	(1,245)
Net cash used in operating activities					(111,519)	(111,658)	(75,874)
Cash flows from investing activities:
Cash paid for asset acquisitions, net of cash acquired					(179,624)	0	0
Purchases of marketable securities					(329,641)	(569,515)	0
Proceeds from maturities of marketable securities					415,020	125,783	0
Proceeds from sale of marketable securities					176,858	0	0
Purchases of property and equipment					(9,492)	(1,018)	(76)
Net cash provided by (used) in investing activities					73,121	(444,750)	(76)
Cash flows from financing activities:
Payment of contingent consideration amounts previously established in purchase accounting					(20,000)	0	0
Principal repayments of long-term debt					0	0	(20,000)
Payment of fees to extinguish long-term debt					0	0	(1,865)
Proceeds from issuance of common stock under equity incentive plans					10,182	9,654	9,176
Taxes paid related to net share settlement of equity awards					(744)	(1,430)	0
Proceeds from issuance of common stock, net of issuance costs					42,576	323,135	290,591
Net cash provided by financing activities					32,014	331,359	277,902
Net (decrease) increase in cash and cash equivalents					(6,384)	(225,049)	201,952
Cash and cash equivalents at beginning of period		$ 68,454		$ 293,503	68,454	293,503	91,551
Cash and cash equivalents at end of period	$ 62,070		$ 68,454		62,070	68,454	293,503	$ 91,551
Supplemental disclosure of cash flow information:
Cash paid for interest					0	0	1,475
Noncash investing and financing activities:
Common stock issued as consideration for asset acquisition					68,124	0	0
Net liabilities assumed in connection with asset acquisition					3,688	0	0
Purchases of property and equipment in accounts payable and accrued liabilities					0	1,762	0
Extinguishment of note payable advanced by a customer under a contract manufacturing supply agreement through net settlement of our receivables from the customer					$ 0	$ 0	$ 7,000