Condensed Consolidated Statements Of Cash Flows - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020
Cash flows from operating activities:
Net income	$ 298,126	$ 486,595
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation of property and equipment	23,577	22,841
Stock-based compensation	26,591	23,428
Other Noncash Income (Expense)	(4,398)	8,101
Changes in operating assets and liabilities
Other assets	(18,602)	(10,146)
Accounts payable and accrued liabilities	(36,787)	25,796
Deferred revenues	49,976	30,430
Deferred Income Taxes	(6,435)	(175,471)
Net cash provided by operating activities	340,844	395,372
Net Cash Provided by (Used in) Investing Activities [Abstract]
Proceeds from maturities and sales of marketable securities	1,482,952	995,194
Purchases of marketable securities	(1,623,566)	(1,167,680)
Payments for (Proceeds from) Businesses and Interest in Affiliates	0	20,009
Purchases of property and equipment	(24,270)	(21,891)
Net cash used in investing activities	(164,884)	(174,368)
Repayments of Debt, Maturing in More than Three Months	(750,000)	0
Proceeds from Debt, Net of Issuance Costs	742,329	0
Cash flows from financing activities:
Proceeds from employee stock purchase plans	8,101	8,296
Repurchases of common stock	(361,199)	(429,826)
Net cash used in financing activities	(360,769)	(421,530)
Effect of Exchange Rate on Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	(364)	(965)
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents, Period Increase (Decrease), Including Exchange Rate Effect	(185,173)	(201,491)
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents, beginning of period	410,601	517,601
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents, end of period	225,428	316,110
Supplemental cash flow disclosures:
Cash paid for interest	48,718	43,708
Cash paid for income taxes, net of refunds received	$ 98,993	$ 26,472