Consolidated Statements of Cash Flows - USD ($)	12 Months Ended			94 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2019
Cash flows from operating activities:
Net income (loss)	$ (440,667,000)	$ 681,313,000	$ (96,692,000)
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	(36,303,000)	(33,308,000)	(30,531,000)	$ (207,142,000)
Non-cash interest expense on liability related to sale of future royalties	25,044,000	21,196,000	18,869,000	166,693,000
Stock-based compensation	99,795,000	88,101,000	36,615,000
Depreciation and amortization	13,156,000	10,870,000	14,741,000
Impairment of equipment from terminated program	0	0	15,081,000
Accretion of discounts, net, and other non-cash transactions	(11,394,000)	(10,952,000)	(881,000)
Changes in operating assets and liabilities:
Accounts receivable	6,411,000	(25,505,000)	10,664,000
Inventory	(1,284,000)	(655,000)	383,000
Operating lease right-of-use assets, net of operating lease liabilities	13,090,000	0	0
Other assets	1,190,000	(31,652,000)	(4,800,000)
Accounts payable	12,967,000	971,000	2,074,000
Accrued compensation	1,530,000	1,674,000	(10,017,000)
Other accrued expenses	3,816,000	27,947,000	7,277,000
Deferred revenue	(16,565,000)	(15,331,000)	(28,269,000)
Other liabilities	533,000	3,545,000	(14,928,000)
Net cash provided by (used in) operating activities	(328,681,000)	718,214,000	(80,414,000)
Cash flows from investing activities:
Purchases of investments	(1,380,865,000)	(2,271,250,000)	(404,425,000)
Maturities of investments	1,614,036,000	890,957,000	347,743,000
Sales of investments	0	11,963,000	37,549,000
Purchases of property, plant and equipment	(26,285,000)	(14,239,000)	(9,676,000)
Sales of property and plant	0	2,633,000	0
Net cash provided by (used in) investing activities	206,886,000	(1,379,936,000)	(28,809,000)
Cash flows from financing activities:
Issuance of common stock to Bristol-Myers Squibb (Note 10)	0	790,231,000	0
Proceeds from shares issued under equity compensation plans	23,355,000	61,735,000	59,522,000
Payment of capital lease obligations	0	0	(5,131,000)
Net cash provided by financing activities	23,355,000	851,966,000	54,391,000
Effect of exchange rates on cash and cash equivalents	(102,000)	(101,000)	(46,000)
Net increase (decrease) in cash and cash equivalents	(98,542,000)	190,143,000	(54,878,000)
Cash and cash equivalents at beginning of year	194,905,000	4,762,000	59,640,000
Cash and cash equivalents at end of year	96,363,000	194,905,000	4,762,000	$ 96,363,000
Supplemental disclosure of cash flow information:
Cash paid for interest	19,199,000	19,471,000	20,116,000
Cash paid for income taxes	555,000	618,000	556,000
Right-of-use assets recognized in exchange for operating lease liabilities	$ 57,691,000	$ 0	$ 0