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Summary Of Significant Accounting Policies (Schedule Of Risk Concentration) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Concentration Risk [Line Items]
Cash and cash equivalents, at carrying value	$ 822,479	$ 784,168	$ 788,064	$ 742,486
Customer Concentration Risk [Member]
Concentration Risk [Line Items]
Channel partner concentration risk, percentage	24.40%	24.20%	24.90%
Credit Concentration Risk [Member]
Concentration Risk [Line Items]
Cash and cash equivalents held in excess of deposit insurance, foreign and domestic	$ 805,374	$ 763,400
Largest balance of cash and cash equivalents held with one financial institution, foreign and domestic	$ 377,602	$ 440,650
1st Largest Channel Partner [Member] \| Customer Concentration Risk [Member]
Concentration Risk [Line Items]
Channel partner concentration risk, percentage	5.00%	5.00%	4.00%
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	$ 593,348	$ 539,031
FOREIGN \| Credit Concentration Risk [Member]
Concentration Risk [Line Items]
Cash and cash equivalents, at carrying value	$ 229,131	$ 245,137