Summary of Investments (Fair Value of Investments) (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Held-to-maturity Securities, Debt Maturities [Abstract]
Cost or Amortized Cost	$ 1,847	$ 4,143
Held-To-Maturity, Fair Value	1,883	4,161
Available-for-sale Securities [Abstract]
Cost or Amortized Cost	2,735,999	2,631,345
Gross Unrealized Appreciation	278,064	232,768
Gross Unrealized Depreciation	3,632	7,414
Available-For-Sale, Fair Value	3,010,431	2,856,699
Debt Securities [Member]
Held-to-maturity Securities, Debt Maturities [Abstract]
Cost or Amortized Cost	1,847	4,143
Gross Unrealized Appreciation	36	79
Gross Unrealized Depreciation	0	61
Held-To-Maturity, Fair Value	1,883	4,161
Available-for-sale Securities [Abstract]
Cost or Amortized Cost	2,667,040	2,562,786
Gross Unrealized Appreciation	166,393	140,030
Gross Unrealized Depreciation	2,726	5,568
Available-For-Sale, Fair Value	2,830,707	2,697,248
U.S. Treasury [Member]
Available-for-sale Securities [Abstract]
Cost or Amortized Cost	44,776	42,530
Gross Unrealized Appreciation	1,096	1,421
Gross Unrealized Depreciation	0	0
Available-For-Sale, Fair Value	45,872	43,951
U.S. Government Agency [Member]
Available-for-sale Securities [Abstract]
Cost or Amortized Cost	27,864	95,813
Gross Unrealized Appreciation	462	582
Gross Unrealized Depreciation	29	0
Available-For-Sale, Fair Value	28,297	96,395
States, Municipalities and Political Subdivisions [Member]
Held-to-maturity Securities, Debt Maturities [Abstract]
Cost or Amortized Cost	1,559	3,739
Gross Unrealized Appreciation	20	52
Gross Unrealized Depreciation	0	61
Held-To-Maturity, Fair Value	1,579	3,730
Available-for-sale Securities [Abstract]
Cost or Amortized Cost	714,000	687,039
Gross Unrealized Appreciation	60,739	61,076
Gross Unrealized Depreciation	63	8
Available-For-Sale, Fair Value	774,676	748,107
Foreign Bonds [Member]
Available-for-sale Securities [Abstract]
Cost or Amortized Cost	209,772	206,872
Gross Unrealized Appreciation	12,301	8,766
Gross Unrealized Depreciation	209	823
Available-For-Sale, Fair Value	221,864	214,815
Public Utilities [Member]
Available-for-sale Securities [Abstract]
Cost or Amortized Cost	245,161	254,822
Gross Unrealized Appreciation	16,045	15,562
Gross Unrealized Depreciation	59	313
Available-For-Sale, Fair Value	261,147	270,071
Corporate Bonds [Member] \| Energy [Member]
Available-for-sale Securities [Abstract]
Cost or Amortized Cost	173,486	189,902
Gross Unrealized Appreciation	9,949	7,567
Gross Unrealized Depreciation	0	277
Available-For-Sale, Fair Value	183,435	197,192
Corporate Bonds [Member] \| Industrial [Member]
Available-for-sale Securities [Abstract]
Cost or Amortized Cost	300,958	285,696
Gross Unrealized Appreciation	15,233	10,631
Gross Unrealized Depreciation	277	650
Available-For-Sale, Fair Value	315,914	295,677
Corporate Bonds [Member] \| Consumer Goods and Service [Member]
Available-for-sale Securities [Abstract]
Cost or Amortized Cost	197,861	203,948
Gross Unrealized Appreciation	10,868	8,872
Gross Unrealized Depreciation	147	646
Available-For-Sale, Fair Value	208,582	212,174
Corporate Bonds [Member] \| Health Care [Member]
Available-for-sale Securities [Abstract]
Cost or Amortized Cost	117,779	109,219
Gross Unrealized Appreciation	7,684	6,497
Gross Unrealized Depreciation	39	45
Available-For-Sale, Fair Value	125,424	115,671
Corporate Bonds [Member] \| Technology, Media and Telecommunications [Member]
Available-for-sale Securities [Abstract]
Cost or Amortized Cost	126,996	108,315
Gross Unrealized Appreciation	7,895	4,951
Gross Unrealized Depreciation	21	318
Available-For-Sale, Fair Value	134,870	112,948
Corporate Bonds [Member] \| Financial Services [Member]
Available-for-sale Securities [Abstract]
Cost or Amortized Cost	284,895	258,526
Gross Unrealized Appreciation	15,571	9,075
Gross Unrealized Depreciation	1,260	2,300
Available-For-Sale, Fair Value	299,206	265,301
Mortgage Backed Securities [Member]
Held-to-maturity Securities, Debt Maturities [Abstract]
Cost or Amortized Cost	267	356
Gross Unrealized Appreciation	16	25
Gross Unrealized Depreciation	0	0
Held-To-Maturity, Fair Value	283	381
Available-for-sale Securities [Abstract]
Cost or Amortized Cost	30,752	34,353
Gross Unrealized Appreciation	1,144	1,041
Gross Unrealized Depreciation	1	4
Available-For-Sale, Fair Value	31,895	35,390
Collateralized Mortgage Obligations [Member]
Held-to-maturity Securities, Debt Maturities [Abstract]
Cost or Amortized Cost	21	48
Gross Unrealized Appreciation	0	2
Gross Unrealized Depreciation	0	0
Held-To-Maturity, Fair Value	21	50
Available-for-sale Securities [Abstract]
Cost or Amortized Cost	187,788	79,545
Gross Unrealized Appreciation	6,990	3,490
Gross Unrealized Depreciation	621	184
Available-For-Sale, Fair Value	194,157	82,851
Asset-Backed Securities [Member]
Available-for-sale Securities [Abstract]
Cost or Amortized Cost	4,574	5,801
Gross Unrealized Appreciation	412	495
Gross Unrealized Depreciation	0	0
Available-For-Sale, Fair Value	4,986	6,296
Redeemable Preferred Stocks [Member]
Available-for-sale Securities [Abstract]
Cost or Amortized Cost	378	405
Gross Unrealized Appreciation	4	4
Gross Unrealized Depreciation	0	0
Available-For-Sale, Fair Value	382	409
Equity Securities [Member]
Available-for-sale Securities [Abstract]
Cost or Amortized Cost	68,959	68,559
Gross Unrealized Appreciation	111,671	92,738
Gross Unrealized Depreciation	906	1,846
Available-For-Sale, Fair Value	179,724	159,451
Common Stocks [Member] \| Public Utilities [Member]
Available-for-sale Securities [Abstract]
Cost or Amortized Cost	7,231	7,231
Gross Unrealized Appreciation	7,376	7,602
Gross Unrealized Depreciation	105	98
Available-For-Sale, Fair Value	14,502	14,735
Common Stocks [Member] \| Energy [Member]
Available-for-sale Securities [Abstract]
Cost or Amortized Cost	5,094	5,094
Gross Unrealized Appreciation	7,346	7,116
Gross Unrealized Depreciation	0	0
Available-For-Sale, Fair Value	12,440	12,210
Common Stocks [Member] \| Industrial [Member]
Available-for-sale Securities [Abstract]
Cost or Amortized Cost	13,030	12,678
Gross Unrealized Appreciation	17,870	16,153
Gross Unrealized Depreciation	217	275
Available-For-Sale, Fair Value	30,683	28,556
Common Stocks [Member] \| Consumer Goods and Service [Member]
Available-for-sale Securities [Abstract]
Cost or Amortized Cost	10,394	10,750
Gross Unrealized Appreciation	8,548	7,982
Gross Unrealized Depreciation	47	168
Available-For-Sale, Fair Value	18,895	18,564
Common Stocks [Member] \| Health Care [Member]
Available-for-sale Securities [Abstract]
Cost or Amortized Cost	8,255	8,212
Gross Unrealized Appreciation	10,996	8,008
Gross Unrealized Depreciation	109	232
Available-For-Sale, Fair Value	19,142	15,988
Common Stocks [Member] \| Technology, Media and Telecommunications [Member]
Available-for-sale Securities [Abstract]
Cost or Amortized Cost	5,367	5,368
Gross Unrealized Appreciation	5,913	4,796
Gross Unrealized Depreciation	124	146
Available-For-Sale, Fair Value	11,156	10,018
Common Stocks [Member] \| Financial Services [Member]
Available-for-sale Securities [Abstract]
Cost or Amortized Cost	15,701	15,592
Gross Unrealized Appreciation	53,588	41,041
Gross Unrealized Depreciation	219	543
Available-For-Sale, Fair Value	69,070	56,090
Nonredeemable Preferred Stocks [Member]
Available-for-sale Securities [Abstract]
Cost or Amortized Cost	3,887	3,634
Gross Unrealized Appreciation	34	40
Gross Unrealized Depreciation	85	384
Available-For-Sale, Fair Value	$ 3,836	$ 3,290

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This item represents the cost of debt and equity securities, which are categorized neither as held-to-maturity nor trading, net of adjustments including accretion, amortization, collection of cash, previous other-than-temporary impairments recognized in earnings (less any cumulative-effect adjustments recognized, as defined), and fair value hedge accounting adjustments, if any.

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