Condensed Consolidated Statements Of Cash Flows - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Cash flows from operating activities:
Net income	$ 134,263	$ 116,412
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation of property and equipment	12,117	13,102
Stock-based compensation	12,978	12,563
Amortization of Debt Issuance Costs and Discounts	3,918	3,493
Accretion (Amortization) of Discounts and Premiums, Investments	(4,128)	(1,764)
Other, net	87	328
Changes in operating assets and liabilities
Other assets	(987)	14,196
Accounts payable and accrued liabilities	(36,271)	(67,608)
Deferred revenues	27,120	36,689
Deferred Income Taxes	(59,108)	20,775
Net cash provided by operating activities	89,989	148,186
Net Cash Provided by (Used in) Investing Activities [Abstract]
Proceeds from maturities and sales of marketable securities	1,931,930	1,049,795
Purchases of marketable securities	(631,456)	(813,459)
Purchases of property and equipment	(7,662)	(9,654)
Other investing activities	(160)	11,748
Net cash used in investing activities	1,292,652	238,430
Cash flows from financing activities:
Proceeds from employee stock purchase plans	7,811	7,997
Repurchases of common stock	(152,741)	(173,048)
Net cash used in financing activities	(144,930)	(165,051)
Effect of exchange rate changes on cash and cash equivalents	167	738
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents, Period Increase (Decrease), Including Exchange Rate Effect	1,237,878	222,303
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents, beginning of period	475,139	241,581
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents, end of period	1,713,017	463,884
Supplemental cash flow disclosures:
Cash paid for interest, net of capitalized interest	43,326	28,189
Cash paid for income taxes, net of refunds received	$ 72,959	$ 17,861