UNAUDITED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017
OPERATING ACTIVITIES:
Net income	$ 1,584,582	$ 1,175,832
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation	117,427	85,123
Amortization	92,329	84,179
Provision for uncollectible accounts	62,033	26,127
Deferred income tax benefit	(21,328)	(40,939)
Net unrealized gains on marketable equity securities	(76,363)	0
Stock-based compensation expense and other stock-based payments	149,501	126,047
Amortization of debt issuance costs	3,793	4,509
Amortization of debt discount	27,371	35,386
Loss on early extinguishment of debt	0	1,027
Changes in assets and liabilities, net of effects of an acquisition:
Accounts receivable	(391,802)	(333,545)
Prepaid expenses and other current assets	(574,151)	(438,641)
Accounts payable, accrued expenses and other current liabilities	1,328,616	873,705
Other long-term assets and liabilities	(11,789)	3,024
Net cash provided by operating activities	2,290,219	1,601,834
INVESTING ACTIVITIES:
Purchase of investments	(1,359,605)	(2,869,903)
Proceeds from sale of investments	3,497,179	1,480,236
Additions to property and equipment	(235,035)	(147,269)
Acquisitions and other investments, net of cash acquired	(139,386)	(490)
Net cash provided by (used in) investing activities	1,763,153	(1,537,426)
FINANCING ACTIVITIES:
Proceeds from short-term borrowing	3,033	4,599
Proceeds from the issuance of long-term debt	0	1,051,722
Payments for conversion of senior notes	(1,487,109)	(83,473)
Payment of debt	(348)	0
Payments for repurchase of common stock	(1,905,280)	(555,250)
Proceeds from exercise of stock options	1,329	2,790
Net cash (used in) provided by financing activities	(3,388,375)	420,388
Effect of exchange rate changes on cash, cash equivalents and restricted cash and cash equivalents	(20,457)	68,570
Net increase in cash, cash equivalents and restricted cash and cash equivalents	644,540	553,366
Cash, cash equivalents and restricted cash and cash equivalents, beginning of period	2,563,341	2,082,007
Cash, cash equivalents and restricted cash and cash equivalents, end of period	3,207,881	2,635,373
SUPPLEMENTAL CASH FLOW INFORMATION:
Cash paid during the period for income taxes	984,524	577,247
Cash paid during the period for interest	100,662	60,308
Non-cash financing activity for loan forgiveness	0	1,000
Non-cash operating and financing activity for an acquisition (see Note 7)	50,751	0
Non-cash investing and financing activity for an acquisition (see Note 7)	$ 59,690	$ 0