Condensed Consolidated Statements Of Cash Flows - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
Cash flows from operating activities:
Net income	$ 454,748	$ 657,574
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation of property and equipment	35,609	34,463
Stock-based compensation	41,019	36,106
Other Noncash Income (Expense)	(5,410)	8,482
Changes in operating assets and liabilities
Other assets	(19,735)	(11,107)
Accounts payable and accrued liabilities	(5,529)	(5,912)
Deferred revenues	94,863	27,673
Deferred Income Taxes	(5,476)	(195,353)
Net cash provided by operating activities	600,909	534,962
Net Cash Provided by (Used in) Investing Activities [Abstract]
Proceeds from maturities and sales of marketable securities	2,246,148	1,804,541
Purchases of marketable securities	(2,421,705)	(2,093,437)
Payments for (Proceeds from) Businesses and Interest in Affiliates	0	20,009
Purchases of property and equipment	(39,536)	(36,933)
Net cash used in investing activities	(215,093)	(305,820)
Repayments of Debt, Maturing in More than Three Months	(750,000)	0
Proceeds from Debt, Net of Issuance Costs	741,075	0
Cash flows from financing activities:
Proceeds from employee stock purchase plans	12,404	12,577
Repurchases of common stock	(536,797)	(603,705)
Net cash used in financing activities	(533,318)	(591,128)
Effect of Exchange Rate on Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	(600)	(506)
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents, Period Increase (Decrease), Including Exchange Rate Effect	(148,102)	(362,492)
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	262,499	155,109
Supplemental cash flow disclosures:
Cash paid for interest	61,845	56,860
Cash paid for income taxes, net of refunds received	$ 132,202	$ 105,258