Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017
Cash flows from operating activities:
Net income	$ 433,551	$ 280,717
Adjustments to reconcile net income to net cash provided by operating activities:
Stock-based compensation expense	160,572	142,534
Depreciation expense	34,402	29,740
Write-downs of inventories to net realizable value	6,928	9,479
Deferred income taxes	3,516	4,626
Impairment of property and equipment	0	1,946
Unrealized gain on equity securities	(149,376)	0
Other non-cash items, net	10,014	(4,834)
Changes in operating assets and liabilities:
Accounts receivable, net	(88,166)	(49,767)
Inventories	(9,366)	(22,998)
Prepaid expenses and other assets	33,408	(39,531)
Accounts payable	12,229	14,047
Accrued expenses and other liabilities	126,648	81,386
Net cash provided by operating activities	574,360	447,345
Cash flows from investing activities:
Purchases of marketable securities	(202,002)
Purchases of marketable securities		(377,667)
Maturities of marketable securities	171,028	168,882
Expenditures for property and equipment	(58,891)	(28,477)
Investment in equity securities	(21,500)	0
Net cash used in investing activities	(111,365)	(237,262)
Cash flows from financing activities:
Issuances of common stock under benefit plans	144,837	147,887
Repurchase of common stock	(115,033)	0
Payments on revolving credit facility	0	(300,000)
Advance from collaborator	5,000	7,500
Payments on capital lease obligations	(14,061)	(10,637)
Proceeds related to construction financing lease obligation	9,566	0
Repayments of advanced funding	(2,412)	(2,044)
Other financing activities	(149)	(238)
Net cash provided by (used in) financing activities	27,748	(157,532)
Effect of changes in exchange rates on cash	(4,201)	3,500
Net increase in cash and cash equivalents	486,542	56,051
Cash, cash equivalents and restricted cash—beginning of period	1,667,526	1,231,707
Cash, cash equivalents and restricted cash—end of period	2,154,068	1,287,758
Supplemental disclosure of cash flow information:
Cash paid for interest	33,444	35,003
Cash paid for income taxes	7,069	2,218
Capitalization of costs related to construction financing lease obligation	5,176	38,930
Issuances of common stock from employee benefit plans receivable	13,634	188
Accrued share repurchase liability	$ 4,001	$ 0