Summary of Investments (Fair Value of Investments) (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Held-to-maturity Securities, Debt Maturities [Abstract]
Cost or Amortized Cost	$ 366us-gaap_HeldToMaturitySecurities	$ 397us-gaap_HeldToMaturitySecurities
Fair Value	370	404
Available-for-sale Securities [Abstract]
Cost or Amortized Cost	2,799,672	2,845,217
Gross Unrealized Appreciation	269,148	257,633
Gross Unrealized Depreciation	7,314	13,928
Fair Value	3,061,506us-gaap_AvailableForSaleSecurities	3,088,922us-gaap_AvailableForSaleSecurities
Fixed Maturities [Member]
Held-to-maturity Securities, Debt Maturities [Abstract]
Cost or Amortized Cost	366	397
Gross Unrealized Appreciation	4	7
Gross Unrealized Depreciation	0	0
Fair Value	370	404
Available-for-sale Securities [Abstract]
Cost or Amortized Cost	2,727,434	2,773,566
Gross Unrealized Appreciation	97,532	82,882
Gross Unrealized Depreciation	7,011	13,369
Fair Value	2,817,955	2,843,079
U.S. Treasury [Member]
Available-for-sale Securities [Abstract]
Cost or Amortized Cost	20,790	25,856
Gross Unrealized Appreciation	287	168
Gross Unrealized Depreciation	6	52
Fair Value	21,071	25,972
U.S. Government Agency [Member]
Available-for-sale Securities [Abstract]
Cost or Amortized Cost	301,686	349,747
Gross Unrealized Appreciation	5,287	4,347
Gross Unrealized Depreciation	582	2,422
Fair Value	306,391	351,672
States, Municipalities and Political Subdivisions [Member]
Held-to-maturity Securities, Debt Maturities [Abstract]
Cost or Amortized Cost	55	55
Gross Unrealized Appreciation	1	0
Gross Unrealized Depreciation	0	0
Fair Value	56	55
Available-for-sale Securities [Abstract]
Cost or Amortized Cost	765,100	748,632
Gross Unrealized Appreciation	30,327	30,395
Gross Unrealized Depreciation	722	742
Fair Value	794,705	778,285
Foreign Bonds [Member]
Available-for-sale Securities [Abstract]
Cost or Amortized Cost	125,431	136,487
Gross Unrealized Appreciation	4,724	4,132
Gross Unrealized Depreciation	468	446
Fair Value	129,687	140,173
Public Utilities [Member]
Available-for-sale Securities [Abstract]
Cost or Amortized Cost	210,251	206,366
Gross Unrealized Appreciation	8,490	6,479
Gross Unrealized Depreciation	228	488
Fair Value	218,513	212,357
Corporate Bonds [Member] \| Energy [Member]
Available-for-sale Securities [Abstract]
Cost or Amortized Cost	117,526	135,068
Gross Unrealized Appreciation	3,554	2,858
Gross Unrealized Depreciation	467	793
Fair Value	120,613	137,133
Corporate Bonds [Member] \| Industrials [Member]
Available-for-sale Securities [Abstract]
Cost or Amortized Cost	205,678	211,256
Gross Unrealized Appreciation	7,967	6,373
Gross Unrealized Depreciation	1,656	2,154
Fair Value	211,989	215,475
Corporate Bonds [Member] \| Consumer Goods and Services [Member]
Available-for-sale Securities [Abstract]
Cost or Amortized Cost	172,644	172,623
Gross Unrealized Appreciation	6,253	4,702
Gross Unrealized Depreciation	175	324
Fair Value	178,722	177,001
Corporate Bonds [Member] \| Health Care [Member]
Available-for-sale Securities [Abstract]
Cost or Amortized Cost	89,689	86,017
Gross Unrealized Appreciation	4,025	3,228
Gross Unrealized Depreciation	29	210
Fair Value	93,685	89,035
Corporate Bonds [Member] \| Technology, Media and Telecommunications [Member]
Available-for-sale Securities [Abstract]
Cost or Amortized Cost	130,242	131,465
Gross Unrealized Appreciation	4,650	3,863
Gross Unrealized Depreciation	345	799
Fair Value	134,547	134,529
Corporate Bonds [Member] \| Financial Services [Member]
Held-to-maturity Securities, Debt Maturities [Abstract]
Cost or Amortized Cost	200	200
Gross Unrealized Appreciation	0	0
Gross Unrealized Depreciation	0	0
Fair Value	200	200
Available-for-sale Securities [Abstract]
Cost or Amortized Cost	221,491	215,095
Gross Unrealized Appreciation	10,252	8,574
Gross Unrealized Depreciation	1	87
Fair Value	231,742	223,582
Mortgage-Backed Securities [Member]
Held-to-maturity Securities, Debt Maturities [Abstract]
Cost or Amortized Cost	111	142
Gross Unrealized Appreciation	3	7
Gross Unrealized Depreciation	0	0
Fair Value	114	149
Available-for-sale Securities [Abstract]
Cost or Amortized Cost	16,243	17,121
Gross Unrealized Appreciation	610	483
Gross Unrealized Depreciation	11	46
Fair Value	16,842	17,558
Collateralized Mortgage Obligations [Member]
Available-for-sale Securities [Abstract]
Cost or Amortized Cost	345,805	335,092
Gross Unrealized Appreciation	10,813	7,003
Gross Unrealized Depreciation	2,321	4,806
Fair Value	354,297	337,289
Asset-Backed Securities [Member]
Available-for-sale Securities [Abstract]
Cost or Amortized Cost	4,858	2,741
Gross Unrealized Appreciation	293	277
Gross Unrealized Depreciation	0	0
Fair Value	5,151	3,018
Equity Securities [Member]
Available-for-sale Securities [Abstract]
Cost or Amortized Cost	72,238	71,651
Gross Unrealized Appreciation	171,616	174,751
Gross Unrealized Depreciation	303	559
Fair Value	243,551	245,843
Common Stocks [Member] \| Public Utilities [Member]
Available-for-sale Securities [Abstract]
Cost or Amortized Cost	7,231	7,231
Gross Unrealized Appreciation	11,913	13,103
Gross Unrealized Depreciation	62	44
Fair Value	19,082	20,290
Common Stocks [Member] \| Energy [Member]
Available-for-sale Securities [Abstract]
Cost or Amortized Cost	5,625	5,094
Gross Unrealized Appreciation	7,949	8,623
Gross Unrealized Depreciation	7	0
Fair Value	13,567	13,717
Common Stocks [Member] \| Industrials [Member]
Available-for-sale Securities [Abstract]
Cost or Amortized Cost	13,284	13,284
Gross Unrealized Appreciation	33,888	32,299
Gross Unrealized Depreciation	162	124
Fair Value	47,010	45,459
Common Stocks [Member] \| Consumer Goods and Services [Member]
Available-for-sale Securities [Abstract]
Cost or Amortized Cost	10,308	10,294
Gross Unrealized Appreciation	13,189	13,295
Gross Unrealized Depreciation	1	275
Fair Value	23,496	23,314
Common Stocks [Member] \| Health Care [Member]
Available-for-sale Securities [Abstract]
Cost or Amortized Cost	7,920	7,920
Gross Unrealized Appreciation	22,039	22,436
Gross Unrealized Depreciation	0	0
Fair Value	29,959	30,356
Common Stocks [Member] \| Technology, Media and Telecommunications [Member]
Available-for-sale Securities [Abstract]
Cost or Amortized Cost	6,207	6,207
Gross Unrealized Appreciation	6,931	7,846
Gross Unrealized Depreciation	28	58
Fair Value	13,110	13,995
Common Stocks [Member] \| Financial Services [Member]
Available-for-sale Securities [Abstract]
Cost or Amortized Cost	16,679	16,637
Gross Unrealized Appreciation	75,500	77,077
Gross Unrealized Depreciation	43	51
Fair Value	92,136	93,663
Nonredeemable Preferred Stocks [Member]
Available-for-sale Securities [Abstract]
Cost or Amortized Cost	4,984	4,984
Gross Unrealized Appreciation	207	72
Gross Unrealized Depreciation	0	7
Fair Value	$ 5,191	$ 5,049

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