Income Taxes - Reconciliation of income taxes (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Reconciliation of income taxes at the U.S. federal statutory rate to the provision for income taxes
Provision (benefit) at U.S. federal statutory rate	$ (48,766)	$ 102,226	$ 24,223
Unbenefited net operating losses and tax credits	105,923	(73,666)	(51,861)
Excess tax benefits related to share-based compensation	(9,750)	(13,418)	(8,233)
Foreign tax rate differential	30,412	25,419	37,061
Non-deductible officer compensation	7,418	5,213	4,114
Foreign-derived intangible income	(22,830)	(9,153)
Other	1,072	3,264	550
Provision for income taxes	63,479	39,885	$ 5,854
Deferred tax assets:
Net operating loss carry forwards	128,088	102,001
Federal and state research credits	305,099	400,550
Capitalized research and development	43,806	46,188
Deferred revenue and accruals	27,467	13,609
Non-cash compensation	75,867	67,345
Acquisition-related contingent consideration	32,658	31,956
Intangibles, net	289,848	92,806
Long term investments	25,968	14,899
Other	26,303	21,885
Total gross deferred tax assets	955,104	791,239
Less valuation allowance for deferred tax assets	(930,209)	(770,497)
Net deferred tax assets	24,895	20,742
Deferred tax liabilities:
Property and equipment	(22,841)	(19,095)
Total gross deferred tax liabilities	(22,841)	(19,095)
Net deferred tax assets	$ 2,054	$ 1,647