CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Cash flows from operating activities:
Net loss	$ (211,070)	$ (39,269)	$ (273,374)	$ (124,731)
Adjustments to reconcile net loss to net cash used in operating activities:
Non-cash share-based compensation expense			24,884	8,696
Non-cash interest expense on mandatorily redeemable preferred shares	3,955	0	3,955	0
Non-cash interest expense on liability related to sale of future royalties	5,151	501	11,964	501
Change in fair value of derivative liability	1,263	0	1,263	0
Change in fair value of warrant liability	0	0	0	1,182
Loss from equity method investment	1,415	641	2,315	1,369
Other non-cash items			271	53
Changes in operating assets and liabilities:
Prepaid expenses and other current assets			(523)	(4,953)
Other assets			(13)	(11)
Accounts payable			2,117	(694)
Accrued expenses			22,385	3,643
Other long-term liabilities			(2,000)	(44)
Net cash used in operating activities			(206,756)	(114,989)
Cash flows from investing activities:
Purchases of property and equipment			(1,448)	(1,501)
Purchase of equity method investment			0	(1,375)
Net cash used in investing activities			(1,448)	(2,876)
Cash flows from financing activities:
Proceeds from issuance of common shares			282,000	55,000
Proceeds from sale of future royalties			0	106,047
Proceeds from issuance of common stock related to sale of future royalties			0	43,953
Proceeds from issuance of mandatorily redeemable preferred shares			125,000	0
Proceeds from exercise of warrants			1,998	0
Payments of issuance costs			(517)	(2,987)
Proceeds from exercise of stock options			1,213	1,836
Net cash provided by financing activities			409,694	203,849
Net increase in cash			201,490	85,984
Cash at beginning of period			264,249	131,468
Cash at end of period	$ 465,739	$ 217,452	465,739	217,452
Supplemental disclosure of cash flow information:
Cash paid for interest			0	0
Cash paid for income taxes			428	23
Supplemental disclosure of non-cash investing and financing activities:
Offering costs included in accounts payable and accrued expenses			$ 633	$ 377