Amount of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates. Excludes cash and cash equivalents within disposal group and discontinued operation.

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Summary Of Significant Accounting Policies (Schedule Of Risk Concentration) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Concentration Risk [Line Items]
Cash and cash equivalents, at carrying value	$ 881,501	$ 822,479	$ 784,168	$ 788,064
Customer Concentration Risk [Member]
Concentration Risk [Line Items]
Channel partner concentration risk, percentage	24.70%	24.40%	24.20%
Credit Concentration Risk [Member]
Concentration Risk [Line Items]
Cash and cash equivalents held in excess of deposit insurance, foreign and domestic	$ 852,138	$ 805,374
Largest balance of cash and cash equivalents held with one financial institution, foreign and domestic	$ 328,902	$ 377,602
1st Largest Channel Partner [Member] \| Customer Concentration Risk [Member]
Concentration Risk [Line Items]
Channel partner concentration risk, percentage	5.00%	5.00%	5.00%
2nd Largest Channel Partner [Member] \| Customer Concentration Risk [Member]
Concentration Risk [Line Items]
Channel partner concentration risk, percentage	2.00%	2.00%	2.00%
United States \| Credit Concentration Risk [Member]
Concentration Risk [Line Items]
Cash and cash equivalents, at carrying value	$ 561,417	$ 593,348
FOREIGN \| Credit Concentration Risk [Member]
Concentration Risk [Line Items]
Cash and cash equivalents, at carrying value	$ 320,084	$ 229,131