Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018
Cash flows from operating activities:
Net income	$ 593,576	$ 562,007
Adjustments to reconcile net income to net cash provided by operating activities:
Stock-based compensation expense	268,898	246,104
Depreciation expense	80,685	53,594
Change in fair value of contingent consideration	2,959	0
Write-downs of inventories to net realizable value	8,650	13,089
Deferred income taxes	94,175	3,595
Unrealized gains on equity securities	(68,862)	(88,217)
Other non-cash items, net	(12,674)	10,701
Changes in operating assets and liabilities:
Accounts receivable, net	(41,444)	(75,167)
Inventories	(45,280)	(24,461)
Prepaid expenses and other assets	(23,709)	31,797
Accounts payable	(12,210)	23,023
Accrued expenses	255,699	167,647
Other liabilities	22,859	31,996
Net cash provided by operating activities	1,123,322	955,708
Cash flows from investing activities:
Purchases of available-for-sale debt securities	(381,739)	(329,367)
Maturities of available-for-sale debt securities	375,145	308,406
Payment to acquire business, net of cash acquired	(245,824)	0
Expenditures for property and equipment	(58,690)	(79,803)
Investment in equity securities	(27,219)	(60,490)
Net cash used in investing activities	(338,327)	(161,254)
Cash flows from financing activities:
Issuances of common stock under benefit plans	144,630	245,754
Repurchases of common stock	(155,953)	(207,038)
Payments on finance leases	(28,879)
Advance from collaborator	10,000	7,500
Repayments of advanced funding	(4,316)	(3,714)
Proceeds related to capital lease and construction financing lease obligations	1,002	12,983
Payments on capital lease and construction financing lease obligations		(24,658)
Other financing activities	(1,132)	(1,000)
Net cash (used in) provided by financing activities	(34,648)	29,827
Effect of changes in exchange rates on cash	(4,009)	(4,756)
Net increase in cash and cash equivalents	746,338	819,525
Cash, cash equivalents and restricted cash—beginning of period	2,658,253	1,667,526
Cash, cash equivalents and restricted cash—end of period	3,404,591	2,487,051
Supplemental disclosure of cash flow information:
Cash paid for interest	41,704	50,017
Cash paid for income taxes	22,838	10,316
Capitalization of costs related to construction financing lease obligation	0	3,389
Issuances of common stock from employee benefit plans receivable	13	5,509
Accrued share repurchase liability	$ 12,001	$ 4,000