Condensed Consolidated Statements Of Cash Flows (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Operating Activities
Net income	$ 110,348	$ 144,259
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation, amortization and other	62,472	51,876
Stock-based compensation expense	65,234	35,723
Deferred income tax expense	23,993	8,160
Effects of exchange rate changes on monetary assets and liabilities denominated in foreign currencies	(1,939)	(1,906)
Other non-cash items	845	3,302
Total adjustments to reconcile net income to net cash provided by operating activities	150,605	97,155
Changes in operating assets and liabilities, net of the effects of acquisitions:
Accounts receivable	204,406	285,104
Inventories	(1,876)	34
Prepaid expenses and other current assets	17,534	(13,494)
Other assets	(15,891)	9,071
Income taxes, net	(49,379)	(35,996)
Accounts payable	6,134	1,828
Accrued expenses and other current liabilities	(81,979)	(52,735)
Deferred revenues	(77,855)	(79,890)
Other liabilities	5,519	2,519
Total changes in operating assets and liabilities, net of the effects of acquisitions	6,613	116,441
Net cash provided by operating activities	267,566	357,855
Investing Activities
Purchases of available-for-sale investments	(7,094)	(125,687)
Proceeds from sales of available-for-sale investments	772,954	358,465
Proceeds from maturities of available-for-sale investments	134,325	95,341
Purchases of property and equipment	(17,277)	(15,997)
Cash paid for acquisitions, net of cash acquired	0	(66,330)
Cash paid for licensing agreements, patents and technology	(590)	(535)
Other	575	3,257
Net cash provided by investing activities	882,893	248,514
Financing Activities
Proceeds from issuance of common stock under stock-based compensation plans	0	70
Repayment of acquired debt	0	(5,674)
Stock repurchases, net	(93,805)	(600,000)
Accelerated stock repurchase program	0	(150,000)
Cash paid for tax withholding on vested stock awards	(17,662)	(13,602)
Cash paid for dividends	(46,024)	0
Net cash used in financing activities	(157,491)	(769,206)
Effect of exchange rate changes on cash and cash equivalents	945	2,404
Change in cash and cash equivalents	993,913	(160,433)
Cash and cash equivalents at beginning of period	618,766	1,115,130
Cash and cash equivalents at end of period	$ 1,612,679	$ 954,697