Consolidated Statements of Cash Flows - USD ($)	12 Months Ended			106 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2020
Cash flows from operating activities:
Net income (loss)	$ (444,440,000)	$ (440,667,000)	$ 681,313,000
Adjustments to reconcile net income (loss) to net cash provided by (used in) operating activities:
Non-cash royalty revenue related to sale of future royalties	(48,563,000)	(36,303,000)	(33,308,000)	$ (255,705,000)
Non-cash interest expense on liability related to sale of future royalties	30,267,000	25,044,000	21,196,000	196,960,000
Stock-based compensation	94,261,000	99,795,000	88,101,000
Depreciation and amortization	14,182,000	13,156,000	10,870,000
Impairment of advance payments to contract manufacturers and equipment for terminated program	20,351,000	0	0
Accretion of premiums (discounts), net and other non-cash transactions	3,943,000	(11,394,000)	(10,952,000)
Changes in operating assets and liabilities
Accounts receivable	1,913,000	6,411,000	(25,505,000)
Inventory	(2,627,000)	(1,284,000)	(655,000)
Operating leases, net	2,743,000	13,090,000	0
Other assets	4,476,000	1,190,000	(31,652,000)
Accounts payable	2,382,000	12,967,000	971,000
Accrued compensation	4,697,000	1,530,000	1,674,000
Other accrued expenses	8,644,000	4,349,000	31,492,000
Deferred revenue	(5,516,000)	(16,565,000)	(15,331,000)
Net cash provided by (used in) operating activities	(313,287,000)	(328,681,000)	718,214,000
Cash flows from investing activities:
Purchases of investments	(987,533,000)	(1,380,865,000)	(2,271,250,000)
Maturities of investments	1,449,304,000	1,614,036,000	890,957,000
Sales of investments	41,700,000	0	11,963,000
Purchases of property, plant and equipment	(7,258,000)	(26,285,000)	(14,239,000)
Sales of property and plant	0	0	2,633,000
Net cash provided by (used in) investing activities	496,213,000	206,886,000	(1,379,936,000)
Cash flows from financing activities:
Issuance of common stock to Bristol-Myers Squibb (Note 10)	0	0	790,231,000
Proceeds from sale of future royalties, net of $3.8 million of transaction costs	146,250,000	0	0
Repayment of senior notes	(250,000,000)	0	0
Proceeds from shares issued under equity compensation plans	23,396,000	23,355,000	61,735,000
Net cash provided by (used in) financing activities	(80,354,000)	23,355,000	851,966,000
Effect of exchange rates on cash and cash equivalents	20,000	(102,000)	(101,000)
Net increase (decrease) in cash and cash equivalents	102,592,000	(98,542,000)	190,143,000
Cash and cash equivalents at beginning of year	96,363,000	194,905,000	4,762,000
Cash and cash equivalents at end of year	198,955,000	96,363,000	194,905,000	$ 198,955,000
Supplemental disclosure of cash flow information:
Cash paid for interest	9,742,000	19,199,000	19,471,000
Cash paid for income taxes	539,000	555,000	618,000
Operating lease right-of-use assets recognized in exchange for lease liabilities	$ 2,133,000	$ 57,691,000	$ 0