Condensed Consolidated Statements Of Cash Flows - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019
Cash flows from operating activities:
Net income	$ 486,595	$ 310,061
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation of property and equipment	22,841	22,884
Stock-based compensation	23,428	25,617
Accretion (Amortization) of Discounts and Premiums, Investments	(5,095)	(5,679)
Other Noncash Income (Expense)	3,006	(894)
Changes in operating assets and liabilities
Other assets	(10,146)	(10,254)
Accounts payable and accrued liabilities	25,796	(39,351)
Deferred revenues	30,430	31,857
Deferred Income Taxes	(175,471)	16,146
Net cash provided by operating activities	395,372	352,175
Net Cash Provided by (Used in) Investing Activities [Abstract]
Proceeds from maturities and sales of marketable securities	995,194	1,466,303
Purchases of marketable securities	(1,167,680)	(1,021,741)
Payments for (Proceeds from) Businesses and Interest in Affiliates	20,009	(6,311)
Purchases of property and equipment	(21,891)	(20,189)
Net cash used in investing activities	(174,368)	418,062
Cash flows from financing activities:
Proceeds from employee stock purchase plans	8,296	8,253
Repurchases of common stock	(429,826)	(384,532)
Net cash used in financing activities	(421,530)	(376,279)
Effect of Exchange Rate on Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	(965)	243
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents, Period Increase (Decrease), Including Exchange Rate Effect	(201,491)	394,201
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents, beginning of period	517,601	366,753
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents, end of period	316,110	760,954
Supplemental cash flow disclosures:
Cash paid for interest	43,708	43,708
Cash paid for income taxes, net of refunds received	$ 26,472	$ 62,214