Summary of Investments (Fair Value of Investments) (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Held-to-maturity Securities, Debt Maturities [Abstract]
Cost or Amortized Cost	$ 1,102	$ 1,655
Held-to-Maturity, Fair Value	1,120	1,681
Available-for-sale Securities [Abstract]
Cost or Amortized Cost	2,795,051	2,724,692
Gross Unrealized Appreciation	225,006	265,081
Gross Unrealized Depreciation	42,437	4,568
Available-for-Sale, Fair Value	2,977,620	2,985,205
Fixed Maturities [Member]
Held-to-maturity Securities, Debt Maturities [Abstract]
Cost or Amortized Cost	1,102	1,655
Gross Unrealized Appreciation	18	26
Gross Unrealized Depreciation	0	0
Held-to-Maturity, Fair Value	1,120	1,681
Available-for-sale Securities [Abstract]
Cost or Amortized Cost	2,724,100	2,657,800
Gross Unrealized Appreciation	86,911	154,146
Gross Unrealized Depreciation	41,929	3,868
Available-for-Sale, Fair Value	2,769,082	2,808,078
U.S. Treasury [Member]
Available-for-sale Securities [Abstract]
Cost or Amortized Cost	35,882	37,887
Gross Unrealized Appreciation	551	939
Gross Unrealized Depreciation	86	5
Available-for-Sale, Fair Value	36,347	38,821
U.S. Government Agency [Member]
Available-for-sale Securities [Abstract]
Cost or Amortized Cost	224,953	45,566
Gross Unrealized Appreciation	449	429
Gross Unrealized Depreciation	11,844	67
Available-for-Sale, Fair Value	213,558	45,928
States, Municipalities and Political Subdivisions [Member]
Held-to-maturity Securities, Debt Maturities [Abstract]
Cost or Amortized Cost	684	1,185
Gross Unrealized Appreciation	7	11
Gross Unrealized Depreciation	0	0
Held-to-Maturity, Fair Value	691	1,196
Available-for-sale Securities [Abstract]
Cost or Amortized Cost	699,796	739,752
Gross Unrealized Appreciation	36,302	55,572
Gross Unrealized Depreciation	9,138	819
Available-for-Sale, Fair Value	726,960	794,505
Foreign Bonds [Member]
Available-for-sale Securities [Abstract]
Cost or Amortized Cost	174,839	207,359
Gross Unrealized Appreciation	6,333	11,863
Gross Unrealized Depreciation	324	62
Available-for-Sale, Fair Value	180,848	219,160
Public Utilities [Member]
Available-for-sale Securities [Abstract]
Cost or Amortized Cost	224,874	232,550
Gross Unrealized Appreciation	8,620	15,208
Gross Unrealized Depreciation	947	32
Available-for-Sale, Fair Value	232,547	247,726
Corporate Bonds [Member] | Energy [Member]
Available-for-sale Securities [Abstract]
Cost or Amortized Cost	154,915	169,973
Gross Unrealized Appreciation	4,802	9,758
Gross Unrealized Depreciation	858	0
Available-for-Sale, Fair Value	158,859	179,731
Corporate Bonds [Member] | Industrials [Member]
Available-for-sale Securities [Abstract]
Cost or Amortized Cost	242,348	280,185
Gross Unrealized Appreciation	6,783	13,690
Gross Unrealized Depreciation	2,257	212
Available-for-Sale, Fair Value	246,874	293,663
Corporate Bonds [Member] | Consumer Goods and Services [Member]
Available-for-sale Securities [Abstract]
Cost or Amortized Cost	176,217	193,313
Gross Unrealized Appreciation	4,544	9,813
Gross Unrealized Depreciation	1,099	151
Available-for-Sale, Fair Value	179,662	202,975
Corporate Bonds [Member] | Health Care [Member]
Available-for-sale Securities [Abstract]
Cost or Amortized Cost	95,424	115,654
Gross Unrealized Appreciation	3,576	7,111
Gross Unrealized Depreciation	1,074	80
Available-for-Sale, Fair Value	97,926	122,685
Corporate Bonds [Member] | Technology, Media and Telecommunications [Member]
Available-for-sale Securities [Abstract]
Cost or Amortized Cost	130,972	123,660
Gross Unrealized Appreciation	2,968	6,909
Gross Unrealized Depreciation	3,203	198
Available-for-Sale, Fair Value	130,737	130,371
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
Held-to-Maturity, Fair Value	200	200
Available-for-sale Securities [Abstract]
Cost or Amortized Cost	241,319	271,061
Gross Unrealized Appreciation	8,921	13,858
Gross Unrealized Depreciation	763	1,059
Available-for-Sale, Fair Value	249,477	283,860
Mortgage-Backed Securities [Member]
Held-to-maturity Securities, Debt Maturities [Abstract]
Cost or Amortized Cost	218	256
Gross Unrealized Appreciation	11	15
Gross Unrealized Depreciation	0	0
Held-to-Maturity, Fair Value	229	271
Available-for-sale Securities [Abstract]
Cost or Amortized Cost	23,641	27,940
Gross Unrealized Appreciation	308	888
Gross Unrealized Depreciation	269	21
Available-for-Sale, Fair Value	23,680	28,807
Collateralized Mortgage Obligations [Member]
Held-to-maturity Securities, Debt Maturities [Abstract]
Cost or Amortized Cost		14
Gross Unrealized Appreciation		0
Gross Unrealized Depreciation		0
Held-to-Maturity, Fair Value		14
Available-for-sale Securities [Abstract]
Cost or Amortized Cost	294,759	208,042
Gross Unrealized Appreciation	2,393	7,702
Gross Unrealized Depreciation	10,067	1,160
Available-for-Sale, Fair Value	287,085	214,584
Asset-Backed Securities [Member]
Available-for-sale Securities [Abstract]
Cost or Amortized Cost	3,827	4,480
Gross Unrealized Appreciation	358	406
Gross Unrealized Depreciation	0	0
Available-for-Sale, Fair Value	4,185	4,886
Redeemable Preferred Stocks [Member]
Available-for-sale Securities [Abstract]
Cost or Amortized Cost	334	378
Gross Unrealized Appreciation	3	0
Gross Unrealized Depreciation	0	2
Available-for-Sale, Fair Value	337	376
Equity Securities [Member]
Available-for-sale Securities [Abstract]
Cost or Amortized Cost	70,951	66,892
Gross Unrealized Appreciation	138,095	110,935
Gross Unrealized Depreciation	508	700
Available-for-Sale, Fair Value	208,538	177,127
Common Stocks [Member] | Public Utilities [Member]
Available-for-sale Securities [Abstract]
Cost or Amortized Cost	7,231	7,231
Gross Unrealized Appreciation	8,543	7,268
Gross Unrealized Depreciation	41	83
Available-for-Sale, Fair Value	15,733	14,416
Common Stocks [Member] | Energy [Member]
Available-for-sale Securities [Abstract]
Cost or Amortized Cost	5,094	5,094
Gross Unrealized Appreciation	8,152	6,903
Gross Unrealized Depreciation	0	0
Available-for-Sale, Fair Value	13,246	11,997
Common Stocks [Member] | Industrials [Member]
Available-for-sale Securities [Abstract]
Cost or Amortized Cost	13,308	13,031
Gross Unrealized Appreciation	27,741	19,827
Gross Unrealized Depreciation	59	174
Available-for-Sale, Fair Value	40,990	32,684
Common Stocks [Member] | Consumer Goods and Services [Member]
Available-for-sale Securities [Abstract]
Cost or Amortized Cost	10,356	10,394
Gross Unrealized Appreciation	9,391	8,535
Gross Unrealized Depreciation	10	50
Available-for-Sale, Fair Value	19,737	18,879
Common Stocks [Member] | Health Care [Member]
Available-for-sale Securities [Abstract]
Cost or Amortized Cost	7,920	7,920
Gross Unrealized Appreciation	13,767	10,286
Gross Unrealized Depreciation	0	125
Available-for-Sale, Fair Value	21,687	18,081
Common Stocks [Member] | Technology, Media and Telecommunications [Member]
Available-for-sale Securities [Abstract]
Cost or Amortized Cost	6,204	5,367
Gross Unrealized Appreciation	6,229	5,155
Gross Unrealized Depreciation	64	95
Available-for-Sale, Fair Value	12,369	10,427
Common Stocks [Member] | Financial Services [Member]
Available-for-sale Securities [Abstract]
Cost or Amortized Cost	15,854	15,701
Gross Unrealized Appreciation	64,267	52,936
Gross Unrealized Depreciation	90	145
Available-for-Sale, Fair Value	80,031	68,492
Nonredeemable Preferred Stocks [Member]
Available-for-sale Securities [Abstract]
Cost or Amortized Cost	4,984	2,154
Gross Unrealized Appreciation	5	25
Gross Unrealized Depreciation	244	28
Available-for-Sale, Fair Value	$ 4,745	$ 2,151