Investments (Gross Unrealized Losses And Fair Value Of Investments) (Details) - USD ($) $ in Thousands	Mar. 31, 2022	Dec. 31, 2021
Less Than Twelve Months
Estimated Fair Value	$ 1,000,744	$ 535,672
Unrealized Loss	58,078	4,966
Estimated Fair Value	7,547	29,918
Twelve Months or Greater
Unrealized Loss	483	437
Estimated Fair Value	1,008,291	565,590
Unrealized Loss	58,561	5,403
Obligations of states and political subdivisions
Less Than Twelve Months
Estimated Fair Value	166,363	13,277
Unrealized Loss	11,280	152
Estimated Fair Value	3,247	2,420
Twelve Months or Greater
Unrealized Loss	209	63
Estimated Fair Value	169,610	15,697
Unrealized Loss	11,489	215
U.S. Government agencies
Less Than Twelve Months
Estimated Fair Value	819,437	521,407
Unrealized Loss	45,995	4,802
Estimated Fair Value	0	23,295
Twelve Months or Greater
Unrealized Loss	0	7
Estimated Fair Value	819,437	544,702
Unrealized Loss	45,995	4,809
Trust preferred securities
Less Than Twelve Months
Estimated Fair Value	0	0
Unrealized Loss	0	0
Estimated Fair Value	4,300	4,203
Twelve Months or Greater
Unrealized Loss	274	367
Estimated Fair Value	4,300	4,203
Unrealized Loss	274	367
Corporate securities
Less Than Twelve Months
Estimated Fair Value	14,944	988
Unrealized Loss	803	12
Estimated Fair Value	0	0
Twelve Months or Greater
Unrealized Loss	0	0
Estimated Fair Value	14,944	988
Unrealized Loss	$ 803	$ 12