Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Cash flows from operating activities:
Net income	$ 602,753	$ 268,631
Adjustments to reconcile net income to net cash provided by operating activities:
Stock-based compensation expense	115,706	93,791
Depreciation expense	26,821	27,140
Increase in fair value of contingent consideration	1,600	0
Deferred income taxes	36,705	43,425
Losses (gains) on equity securities	44,870	(43,551)
Other non-cash items, net	9,668	(2,431)
Changes in operating assets and liabilities:
Accounts receivable, net	(223,672)	(30,136)
Inventories	(27,450)	(13,139)
Prepaid expenses and other assets	2,790	7,941
Accounts payable	14,285	(24,145)
Accrued expenses	153,814	(27,279)
Other liabilities	57,808	24,537
Net cash provided by operating activities	815,698	324,784
Cash flows from investing activities:
Purchases of available-for-sale debt securities	(75,265)	(128,215)
Maturities of available-for-sale debt securities	60,145	107,118
Sale of equity securities	72,036	0
Expenditures for property and equipment	(19,450)	(18,041)
Investment in equity securities	(5,800)	0
Net cash provided by (used in) investing activities	31,666	(39,138)
Cash flows from financing activities:
Issuances of common stock under benefit plans	79,597	63,620
Repurchases of common stock	(300,026)	(94,007)
Payments in connection with common stock withheld for employee tax obligations	(136,167)	(5,832)
Payments on finance leases	(10,287)	(9,385)
Proceeds related to finance leases	5,833	0
Advance from collaborator	2,500	5,000
Repayments of advanced funding	(880)	(1,385)
Net cash used in financing activities	(359,430)	(41,989)
Effect of changes in exchange rates on cash	(6,651)	(378)
Net increase in cash and cash equivalents	481,283	243,279
Cash, cash equivalents and restricted cash—beginning of period	3,120,681	2,658,253
Cash, cash equivalents and restricted cash—end of period	3,601,964	2,901,532
Supplemental disclosure of cash flow information:
Cash paid for interest	13,771	13,148
Cash paid for income taxes	5,845	1,835
Issuances of common stock from employee benefit plans receivable	817	510
Accrued share repurchase liability	$ 0	$ 4,000