Fair Value Measurements (Financial Assets And Liabilities Measured At Fair Value On Recurring Basis) (Details) (Fair Value, Measurements, Recurring [Member], USD $) In Thousands, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available-for-sale securities	$ 1,805,205	$ 1,728,204
Derivative instruments, Assets	32,071	37,320
Total, Assets	1,837,276	1,765,524
Derivative instruments, Liabilities	35,010	22,906
Total, Liabilities	35,010	22,906
Quoted Prices In Active Markets For Identical Assets (Level 1) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available-for-sale securities		54,926
Derivative instruments, Assets
Total, Assets		54,926
Derivative instruments, Liabilities
Total, Liabilities
Significant Other Observable Inputs (Level 2) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available-for-sale securities	1,804,120	1,673,278
Derivative instruments, Assets	32,071	37,320
Total, Assets	1,836,191	1,710,598
Derivative instruments, Liabilities	35,010	22,906
Total, Liabilities	35,010	22,906
Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available-for-sale securities	1,085
Derivative instruments, Assets
Total, Assets	1,085
Derivative instruments, Liabilities
Total, Liabilities