Summary of Investments (Fair Value of Investments) (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2012	Dec. 31, 2011
Held-to-maturity Securities, Debt Maturities [Abstract]
Cost or Amortized Cost	$ 3,864	$ 4,143
Held-To-Maturity, Fair Value	3,927	4,161
Available-for-sale Securities [Abstract]
Cost or Amortized Cost	2,726,601	2,631,345
Gross Unrealized Appreciation	253,772	232,768
Gross Unrealized Depreciation	5,390	7,414
Available-For-Sale, Fair Value	2,974,983	2,856,699
Debt Securities [Member]
Held-to-maturity Securities, Debt Maturities [Abstract]
Cost or Amortized Cost	3,864	4,143
Gross Unrealized Appreciation	63	79
Gross Unrealized Depreciation	0	61
Held-To-Maturity, Fair Value	3,927	4,161
Available-for-sale Securities [Abstract]
Cost or Amortized Cost	2,657,938	2,562,786
Gross Unrealized Appreciation	146,726	140,030
Gross Unrealized Depreciation	4,040	5,568
Available-For-Sale, Fair Value	2,800,624	2,697,248
U.S. Treasury [Member]
Available-for-sale Securities [Abstract]
Cost or Amortized Cost	42,364	42,530
Gross Unrealized Appreciation	1,140	1,421
Gross Unrealized Depreciation	0	0
Available-For-Sale, Fair Value	43,504	43,951
U.S. Government Agency [Member]
Available-for-sale Securities [Abstract]
Cost or Amortized Cost	39,722	95,813
Gross Unrealized Appreciation	490	582
Gross Unrealized Depreciation	0	0
Available-For-Sale, Fair Value	40,212	96,395
States, Municipalities and Political Subdivisions [Member]
Held-to-maturity Securities, Debt Maturities [Abstract]
Cost or Amortized Cost	3,556	3,739
Gross Unrealized Appreciation	44	52
Gross Unrealized Depreciation	0	61
Held-To-Maturity, Fair Value	3,600	3,730
Available-for-sale Securities [Abstract]
Cost or Amortized Cost	699,803	687,039
Gross Unrealized Appreciation	58,080	61,076
Gross Unrealized Depreciation	269	8
Available-For-Sale, Fair Value	757,614	748,107
Foreign Bonds [Member]
Available-for-sale Securities [Abstract]
Cost or Amortized Cost	226,172	206,872
Gross Unrealized Appreciation	10,089	8,766
Gross Unrealized Depreciation	627	823
Available-For-Sale, Fair Value	235,634	214,815
Public Utilities [Member]
Available-for-sale Securities [Abstract]
Cost or Amortized Cost	241,811	254,822
Gross Unrealized Appreciation	15,203	15,562
Gross Unrealized Depreciation	55	313
Available-For-Sale, Fair Value	256,959	270,071
Corporate Bonds [Member] \| Energy [Member]
Available-for-sale Securities [Abstract]
Cost or Amortized Cost	178,831	189,902
Gross Unrealized Appreciation	7,718	7,567
Gross Unrealized Depreciation	1	277
Available-For-Sale, Fair Value	186,548	197,192
Corporate Bonds [Member] \| Industrial [Member]
Available-for-sale Securities [Abstract]
Cost or Amortized Cost	307,282	285,696
Gross Unrealized Appreciation	12,987	10,631
Gross Unrealized Depreciation	484	650
Available-For-Sale, Fair Value	319,785	295,677
Corporate Bonds [Member] \| Consumer Goods and Service [Member]
Available-for-sale Securities [Abstract]
Cost or Amortized Cost	209,643	203,948
Gross Unrealized Appreciation	9,232	8,872
Gross Unrealized Depreciation	271	646
Available-For-Sale, Fair Value	218,604	212,174
Corporate Bonds [Member] \| Health Care [Member]
Available-for-sale Securities [Abstract]
Cost or Amortized Cost	120,500	109,219
Gross Unrealized Appreciation	7,130	6,497
Gross Unrealized Depreciation	7	45
Available-For-Sale, Fair Value	127,623	115,671
Corporate Bonds [Member] \| Technology, Media and Telecommunications [Member]
Available-for-sale Securities [Abstract]
Cost or Amortized Cost	123,527	108,315
Gross Unrealized Appreciation	5,910	4,951
Gross Unrealized Depreciation	106	318
Available-For-Sale, Fair Value	129,331	112,948
Corporate Bonds [Member] \| Financial Services [Member]
Available-for-sale Securities [Abstract]
Cost or Amortized Cost	299,318	258,526
Gross Unrealized Appreciation	10,538	9,075
Gross Unrealized Depreciation	1,746	2,300
Available-For-Sale, Fair Value	308,110	265,301
Mortgage Backed Securities [Member]
Held-to-maturity Securities, Debt Maturities [Abstract]
Cost or Amortized Cost	280	356
Gross Unrealized Appreciation	18	25
Gross Unrealized Depreciation	0	0
Held-To-Maturity, Fair Value	298	381
Available-for-sale Securities [Abstract]
Cost or Amortized Cost	33,884	34,353
Gross Unrealized Appreciation	1,130	1,041
Gross Unrealized Depreciation	22	4
Available-For-Sale, Fair Value	34,992	35,390
Collateralized Mortgage Obligations [Member]
Held-to-maturity Securities, Debt Maturities [Abstract]
Cost or Amortized Cost	28	48
Gross Unrealized Appreciation	1	2
Gross Unrealized Depreciation	0	0
Held-To-Maturity, Fair Value	29	50
Available-for-sale Securities [Abstract]
Cost or Amortized Cost	129,515	79,545
Gross Unrealized Appreciation	6,644	3,490
Gross Unrealized Depreciation	301	184
Available-For-Sale, Fair Value	135,858	82,851
Asset-Backed Securities [Member]
Available-for-sale Securities [Abstract]
Cost or Amortized Cost	5,188	5,801
Gross Unrealized Appreciation	432	495
Gross Unrealized Depreciation	151	0
Available-For-Sale, Fair Value	5,469	6,296
Redeemable Preferred Stocks [Member]
Available-for-sale Securities [Abstract]
Cost or Amortized Cost	378	405
Gross Unrealized Appreciation	3	4
Gross Unrealized Depreciation	0	0
Available-For-Sale, Fair Value	381	409
Equity Securities [Member]
Available-for-sale Securities [Abstract]
Cost or Amortized Cost	68,663	68,559
Gross Unrealized Appreciation	107,046	92,738
Gross Unrealized Depreciation	1,350	1,846
Available-For-Sale, Fair Value	174,359	159,451
Common Stocks [Member] \| Public Utilities [Member]
Available-for-sale Securities [Abstract]
Cost or Amortized Cost	7,231	7,231
Gross Unrealized Appreciation	7,952	7,602
Gross Unrealized Depreciation	172	98
Available-For-Sale, Fair Value	15,011	14,735
Common Stocks [Member] \| Energy [Member]
Available-for-sale Securities [Abstract]
Cost or Amortized Cost	5,094	5,094
Gross Unrealized Appreciation	6,679	7,116
Gross Unrealized Depreciation	0	0
Available-For-Sale, Fair Value	11,773	12,210
Common Stocks [Member] \| Industrial [Member]
Available-for-sale Securities [Abstract]
Cost or Amortized Cost	13,032	12,678
Gross Unrealized Appreciation	18,206	16,153
Gross Unrealized Depreciation	240	275
Available-For-Sale, Fair Value	30,998	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	7,701	7,982
Gross Unrealized Depreciation	134	168
Available-For-Sale, Fair Value	17,961	18,564
Common Stocks [Member] \| Health Care [Member]
Available-for-sale Securities [Abstract]
Cost or Amortized Cost	8,212	8,212
Gross Unrealized Appreciation	10,018	8,008
Gross Unrealized Depreciation	187	232
Available-For-Sale, Fair Value	18,043	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	5,822	4,796
Gross Unrealized Depreciation	134	146
Available-For-Sale, Fair Value	11,055	10,018
Common Stocks [Member] \| Financial Services [Member]
Available-for-sale Securities [Abstract]
Cost or Amortized Cost	15,699	15,592
Gross Unrealized Appreciation	50,549	41,041
Gross Unrealized Depreciation	342	543
Available-For-Sale, Fair Value	65,906	56,090
Nonredeemable Preferred Stocks [Member]
Available-for-sale Securities [Abstract]
Cost or Amortized Cost	3,634	3,634
Gross Unrealized Appreciation	119	40
Gross Unrealized Depreciation	141	384
Available-For-Sale, Fair Value	$ 3,612	$ 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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This item represents the aggregate fair value of investments in debt securities as of the balance sheet date and which are categorized as held-to-maturity.

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