Fair Value Measurements (Summary Of Assets And Liabilities Measured At Fair Value On A Recurring Basis) (Details) (USD $)	Dec. 31, 2014	Dec. 31, 2013
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Repossessed Assets	$ 13,400,000	$ 13,800,000
Fair Value, Measurements, Nonrecurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Repossessed Assets	13,400,000	13,800,000
Fair Value, Measurements, Recurring [Member] | Estimate of Fair Value Measurement [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	737,024,000	836,387,000
Marketable securities	91,140,000	129,181,000
Derivatives	32,244,000	1,932,000
Assets, Fair Value Disclosure	860,408,000	967,500,000
Derivatives, Liabilities	2,027,000	3,925,000
Fair Value, Measurements, Recurring [Member] | Quoted Prices In Active Markets For Identical Assets (Level 1) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	482,686,000	516,173,000
Marketable securities	33,815,000	30,172,000
Derivatives	0	0
Assets, Fair Value Disclosure	516,501,000	546,345,000
Derivatives, Liabilities	0	0
Fair Value, Measurements, Recurring [Member] | Significant Other Observable Inputs (Level 2) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	254,338,000	320,214,000
Marketable securities	57,325,000	99,009,000
Derivatives	32,244,000	1,932,000
Assets, Fair Value Disclosure	343,907,000	421,155,000
Derivatives, Liabilities	2,027,000	3,925,000
Fair Value, Measurements, Recurring [Member] | Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	0	0
Marketable securities	0	0
Derivatives	0	0
Assets, Fair Value Disclosure	0	0
Derivatives, Liabilities	0	0
Fair value, adjustment [Domain]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Repossessed Assets	$ 5,000,000	$ 6,600,000