CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Cash flows from operating activities:
Net income (loss)	$ (295,697)	$ 446,906	$ 109,493
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	51,807	54,533	54,969
Stock-based compensation	177,877	166,589	148,153
Deferred income taxes	(350)	(377)	(459)
Other, net	546	486	344
Unrealized gain (loss) on long term investments	(10,426)	(34,458)	44,093
Change in fair value of acquisition-related contingent consideration	23,385	19,682	26,173
Changes in operating assets and liabilities:
Accounts receivable	(173,185)	(1,211)	(41,299)
Prepaid expenses and other assets	(8,050)	5,744	(33,412)
Inventory	(19,468)	(6,100)	4,043
Accounts payable	15,120	(20,180)	36,156
Accrued and other liabilities	113,842	79,042	(12,027)
Net cash (used in) provided by operating activities	(124,599)	710,656	336,227
Cash flows from investing activities:
Purchase of long term investments	(95,468)		(8,936)
Sale of long term investment	17,250
Capital expenditures	(187,379)	(78,064)	(73,483)
Purchases of marketable securities	(516,874)	(374,809)	(159,932)
Sale and maturities of marketable securities	513,470	365,419	155,928
Net cash used in investing activities	(269,001)	(87,454)	(86,423)
Cash flows from financing activities:
Proceeds from issuance of common stock under stock plans	110,305	63,299	29,942
Payment of finance lease liabilities	(836)	(822)
Payment of contingent consideration	(37,760)	(16,766)	(15,285)
Net cash provided by financing activities	71,709	45,711	14,657
Effect of exchange rates on cash, cash equivalents, restricted cash and investments	2,949	(192)	91
Net (decrease) increase in cash, cash equivalents, restricted cash and investments	(318,942)	668,721	264,552
Cash, cash equivalents, restricted cash and investments at beginning of period	1,833,707	1,164,986	900,434
Cash, cash equivalents, restricted cash and investments at end of period	1,514,765	1,833,707	1,164,986
Supplemental Schedule of Cash Flow Information
Interest paid	194	239	268
Income taxes paid	70,712	33,553	5,417
Unpaid purchases of property and equipment	22,807	12,732	7,673
Leased assets obtained in exchange for new operating lease liabilities	19,908	7,607
Leased assets obtained in exchange for new finance lease liabilities	2,160	$ 29,889
Convertible Senior Notes 0.375 Percent Due 2018
Supplemental Schedule of Cash Flow Information
Reclassification to common stock and additional paid in capital in connection with conversion/exchange of debt instruments			$ 7,695
Convertible Senior Notes 1.25 Percent Due 2020
Supplemental Schedule of Cash Flow Information
Reclassification to common stock and additional paid in capital in connection with conversion/exchange of debt instruments	$ 18,999