Securities in an Unrealized Loss Position (Securities in an Unrealized Loss Position) (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Fair Value, Less than 12 Months	$ 1,080,605	$ 1,221,105
Gross Unrealized Losses, Less than 12 Months	10,434	11,595
Fair Value, 12 Months or Greater	238,937	315,818
Gross Unrealized Losses, 12 Months or Greater	19,785	23,423
Fair Value, Total	1,319,542	1,536,923
Gross Unrealized Losses, Total	30,219	35,018
U.S. Government And Government Agency [Member]
Fair Value, Less than 12 Months	24,203	69,551
Gross Unrealized Losses, Less than 12 Months	58	1,660
Fair Value, 12 Months or Greater	0	0
Gross Unrealized Losses, 12 Months or Greater	0	0
Fair Value, Total	24,203	69,551
Gross Unrealized Losses, Total	58	1,660
State And Municipal [Member]
Fair Value, Less than 12 Months	133,592	152,694
Gross Unrealized Losses, Less than 12 Months	1,830	1,639
Fair Value, 12 Months or Greater	100,664	135,967
Gross Unrealized Losses, 12 Months or Greater	7,389	8,054
Fair Value, Total	234,256	288,661
Gross Unrealized Losses, Total	9,219	9,693
Mortgage-Backed Securities [Member]
Fair Value, Less than 12 Months	451,452	484,731
Gross Unrealized Losses, Less than 12 Months	4,235	3,629
Fair Value, 12 Months or Greater	44,419	58,292
Gross Unrealized Losses, 12 Months or Greater	3,041	4,571
Fair Value, Total	495,871	543,023
Gross Unrealized Losses, Total	7,276	8,200
Corporate [Member]
Fair Value, Less than 12 Months	348,050	371,781
Gross Unrealized Losses, Less than 12 Months	2,425	2,964
Fair Value, 12 Months or Greater	66,309	70,537
Gross Unrealized Losses, 12 Months or Greater	7,955	9,119
Fair Value, Total	414,359	442,318
Gross Unrealized Losses, Total	10,380	12,083
Foreign [Member]
Fair Value, Less than 12 Months	91,803	95,623
Gross Unrealized Losses, Less than 12 Months	309	996
Fair Value, 12 Months or Greater	3,221	11,210
Gross Unrealized Losses, 12 Months or Greater	50	28
Fair Value, Total	95,024	106,833
Gross Unrealized Losses, Total	359	1,024
Fixed Maturity Securities [Member]
Fair Value, Less than 12 Months	1,049,100	1,174,380
Gross Unrealized Losses, Less than 12 Months	8,857	10,888
Fair Value, 12 Months or Greater	214,613	276,006
Gross Unrealized Losses, 12 Months or Greater	18,435	21,772
Fair Value, Total	1,263,713	1,450,386
Gross Unrealized Losses, Total	27,292	32,660
Common Stock [Member]
Fair Value, Less than 12 Months	31,119	46,725
Gross Unrealized Losses, Less than 12 Months	1,342	707
Fair Value, 12 Months or Greater	0	0
Gross Unrealized Losses, 12 Months or Greater	0	0
Fair Value, Total	31,119	46,725
Gross Unrealized Losses, Total	1,342	707
Preferred Stock [Member]
Fair Value, Less than 12 Months	386	0
Gross Unrealized Losses, Less than 12 Months	235	0
Fair Value, 12 Months or Greater	24,324	39,812
Gross Unrealized Losses, 12 Months or Greater	1,350	1,651
Fair Value, Total	24,710	39,812
Gross Unrealized Losses, Total	1,585	1,651
Equity Securities Available For Sale [Member]
Fair Value, Less than 12 Months	31,505	46,725
Gross Unrealized Losses, Less than 12 Months	1,577	707
Fair Value, 12 Months or Greater	24,324	39,812
Gross Unrealized Losses, 12 Months or Greater	1,350	1,651
Fair Value, Total	55,829	86,537
Gross Unrealized Losses, Total	$ 2,927	$ 2,358