Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019
Cash flows from operating activities:
Net income	$ 1,440,023	$ 536,058
Adjustments to reconcile net income to net cash provided by operating activities:
Stock-based compensation expense	232,895	183,478
Depreciation expense	53,518	54,838
Increase in fair value of contingent consideration	10,800	0
Deferred income taxes	8,963	87,358
Gains on equity securities	(65,116)	(100,078)
Other non-cash items, net	16,307	6,006
Changes in operating assets and liabilities:
Accounts receivable, net	(164,139)	(55,870)
Inventories	(64,386)	(25,174)
Prepaid expenses and other assets	(28,923)	(17,580)
Accounts payable	14,697	(28,074)
Accrued expenses	369,851	113,968
Other liabilities	29,735	33,603
Net cash provided by operating activities	1,854,225	788,533
Cash flows from investing activities:
Purchases of available-for-sale debt securities	(126,577)	(263,636)
Maturities of available-for-sale debt securities	145,395	228,707
Sale of equity securities	127,874	0
Expenditures for property and equipment	(37,314)	(34,399)
Investment in equity securities	(5,800)	(20,000)
Net cash provided by (used in) investing activities	103,578	(89,328)
Cash flows from financing activities:
Issuances of common stock under benefit plans	213,058	114,092
Repurchases of common stock	(300,026)	(150,017)
Payments in connection with common stock withheld for employee tax obligations	(139,247)	(5,832)
Payments on finance leases	(20,730)	(18,926)
Proceeds related to finance leases	5,833	1,002
Advance from collaborator	3,500	7,500
Repayments of advanced funding	(1,793)	(2,823)
Net cash used in financing activities	(239,405)	(55,004)
Effect of changes in exchange rates on cash	(3,379)	(808)
Net increase in cash and cash equivalents	1,715,019	643,393
Cash, cash equivalents and restricted cash—beginning of period	3,120,681	2,658,253
Cash, cash equivalents and restricted cash—end of period	4,835,700	3,301,646
Supplemental disclosure of cash flow information:
Cash paid for interest	27,347	27,109
Cash paid for income taxes	36,813	10,902
Issuances of common stock from employee benefit plans receivable	$ 137	$ 539