Consolidated Statements Of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Cash flows from operating activities:
Net income	$ 612,299	$ 582,489	$ 457,248
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation of property and equipment	46,330	48,367	49,878
Stock-based compensation	50,626	52,504	52,907
Investment Income, Amortization of Discount	(14,777)	(18,259)	(14,860)
Gain on Disposition of Business	(817)	(54,840)	(10,421)
Other Operating Activities, Cash Flow Statement	3,668	14,646	272
Changes in operating assets and liabilities
Prepaid expenses and other assets	3,279	(1,041)	(13,775)
Accounts payable and accrued liabilities	(24)	(2,130)	15,483
Deferred revenues	16,191	19,825	25,348
Net deferred income taxes and other long term tax liabilities	43,675	54,124	113,131
Net Cash Provided by (Used in) Operating Activities	753,892	697,767	702,761
Cash flows from investing activities:
Proceeds from maturities and sales of marketable securities	2,247,904	4,031,809	4,562,161
Purchases of marketable securities	(2,030,521)	(2,976,752)	(4,929,834)
Purchases of property and equipment	(40,316)	(37,007)	(49,499)
Payments for (Proceeds from) Businesses and Interest in Affiliates	(9,872)	52,240	11,748
Other investing activities	0	(160)	0
Net cash provided by (used in) investing activities	167,195	1,070,130	(405,424)
Cash flows from financing activities:
Repurchases of common stock	(782,583)	(638,152)	(621,173)
Proceeds from issuance of common stock from option exercises and employee stock purchase plans	13,152	12,836	12,915
Repayments of Subordinated Debt	0	(1,250,009)	0
Proceeds received from borrowing	0	0	543,185
Proceeds from (Payments for) Other Financing Activities	(872)	0	0
Net cash used in financing activities	(770,303)	(1,875,325)	(65,073)
Effect of exchange rate changes on cash and cash equivalents	64	(958)	1,294
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents, Period Increase (Decrease), Including Exchange Rate Effect	150,848	(108,386)	233,558
Cash and cash equivalents at end of period	508,196	357,415
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	517,601	366,753	475,139
Supplemental cash flow disclosures:
Cash paid for interest, net of capitalized interest	87,683	117,956	117,234
Cash paid for income taxes, net of refunds received	$ 89,974	$ 84,906	$ 28,294