Description Of Business And Summary Of Significant Accounting Policies (Narrative) (Details) - USD ($)	1 Months Ended	12 Months Ended
	Aug. 31, 2007	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Mar. 27, 2015	Apr. 16, 2013	Aug. 15, 2007
Description Of Business And Summary Of Significant Accounting Policies [Line Items]
Convertible debenture, interest rate					5.25%	4.625%	3.25%
Convertible debenture, maturity date	Aug. 15, 2037
Net remeasurement gain (loss) on foreign currency translation		$ 1,000,000	$ 1,000,000
Gains (losses) on foreign currency forward contracts		1,000,000	1,000,000
Advertising expenses		17,200,000	16,000,000	$ 20,200,000
Derivative, Notional Amount		39,200,000
Deferred Tax Liabilities, Net, Noncurrent		$ 371,433,000	$ 294,194,000
Building Improvements [Member]
Description Of Business And Summary Of Significant Accounting Policies [Line Items]
Estimated useful life of property and equipment (years)		10 years
Maximum [Member]
Description Of Business And Summary Of Significant Accounting Policies [Line Items]
RegistrationTerm		10 years
Average Service Term		2 years
Maximum [Member] | Buildings [Member]
Description Of Business And Summary Of Significant Accounting Policies [Line Items]
Estimated useful life of property and equipment (years)		47 years
Maximum [Member] | Computer Equipment, Purchased Software, Office Equipment, And Furniture And Fixtures [Member]
Description Of Business And Summary Of Significant Accounting Policies [Line Items]
Estimated useful life of property and equipment (years)		5 years
Minimum [Member]
Description Of Business And Summary Of Significant Accounting Policies [Line Items]
RegistrationTerm		1 year
Average Service Term		1 year
Minimum [Member] | Buildings [Member]
Description Of Business And Summary Of Significant Accounting Policies [Line Items]
Estimated useful life of property and equipment (years)		35 years
Minimum [Member] | Computer Equipment, Purchased Software, Office Equipment, And Furniture And Fixtures [Member]
Description Of Business And Summary Of Significant Accounting Policies [Line Items]
Estimated useful life of property and equipment (years)		3 years