Summary of Investments (Fair Value of Investments) (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Held-to-maturity Securities, Debt Maturities [Abstract]
Cost or Amortized Cost	$ 644	$ 656
Fair Value	656	669
Available-for-sale Securities [Abstract]
Cost or Amortized Cost	2,830,482	2,804,514
Gross Unrealized Appreciation	242,662	235,940
Gross Unrealized Depreciation	35,044	59,830
Fair Value	3,038,100	2,980,624
Fixed Maturities [Member]
Held-to-maturity Securities, Debt Maturities [Abstract]
Cost or Amortized Cost	644	656
Gross Unrealized Appreciation	12	13
Gross Unrealized Depreciation	0	0
Fair Value	656	669
Available-for-sale Securities [Abstract]
Cost or Amortized Cost	2,759,461	2,733,557
Gross Unrealized Appreciation	81,076	77,082
Gross Unrealized Depreciation	34,814	59,383
Fair Value	2,805,723	2,751,256
U.S. Treasury [Member]
Available-for-sale Securities [Abstract]
Cost or Amortized Cost	32,539	33,612
Gross Unrealized Appreciation	346	423
Gross Unrealized Depreciation	130	140
Fair Value	32,755	33,895
U.S. Government Agency [Member]
Available-for-sale Securities [Abstract]
Cost or Amortized Cost	319,146	287,988
Gross Unrealized Appreciation	1,175	258
Gross Unrealized Depreciation	11,641	18,663
Fair Value	308,680	269,583
States, Municipalities and Political Subdivisions [Member]
Held-to-maturity Securities, Debt Maturities [Abstract]
Cost or Amortized Cost	249	250
Gross Unrealized Appreciation	4	4
Gross Unrealized Depreciation	0	0
Fair Value	253	254
Available-for-sale Securities [Abstract]
Cost or Amortized Cost	699,631	690,461
Gross Unrealized Appreciation	33,156	34,151
Gross Unrealized Depreciation	5,191	10,705
Fair Value	727,596	713,907
Foreign Bonds [Member]
Available-for-sale Securities [Abstract]
Cost or Amortized Cost	157,747	167,390
Gross Unrealized Appreciation	6,096	5,863
Gross Unrealized Depreciation	104	397
Fair Value	163,739	172,856
Public Utilities [Member]
Available-for-sale Securities [Abstract]
Cost or Amortized Cost	209,721	213,479
Gross Unrealized Appreciation	6,719	6,873
Gross Unrealized Depreciation	764	1,776
Fair Value	215,676	218,576
Corporate Bonds [Member] | Energy [Member]
Available-for-sale Securities [Abstract]
Cost or Amortized Cost	156,177	157,620
Gross Unrealized Appreciation	4,667	4,398
Gross Unrealized Depreciation	682	1,008
Fair Value	160,162	161,010
Corporate Bonds [Member] | Industrials [Member]
Available-for-sale Securities [Abstract]
Cost or Amortized Cost	227,612	234,221
Gross Unrealized Appreciation	6,220	5,626
Gross Unrealized Depreciation	1,209	2,819
Fair Value	232,623	237,028
Corporate Bonds [Member] | Consumer Goods and Services [Member]
Available-for-sale Securities [Abstract]
Cost or Amortized Cost	171,884	165,565
Gross Unrealized Appreciation	4,454	3,770
Gross Unrealized Depreciation	597	1,421
Fair Value	175,741	167,914
Corporate Bonds [Member] | Health Care [Member]
Available-for-sale Securities [Abstract]
Cost or Amortized Cost	82,693	91,008
Gross Unrealized Appreciation	3,400	3,138
Gross Unrealized Depreciation	552	1,200
Fair Value	85,541	92,946
Corporate Bonds [Member] | Technology, Media and Telecommunications [Member]
Available-for-sale Securities [Abstract]
Cost or Amortized Cost	119,579	121,746
Gross Unrealized Appreciation	3,198	2,541
Gross Unrealized Depreciation	1,516	3,321
Fair Value	121,261	120,966
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	241,936	234,739
Gross Unrealized Appreciation	8,780	7,735
Gross Unrealized Depreciation	272	723
Fair Value	250,444	241,751
Mortgage-Backed Securities [Member]
Held-to-maturity Securities, Debt Maturities [Abstract]
Cost or Amortized Cost	195	206
Gross Unrealized Appreciation	8	9
Gross Unrealized Depreciation	0	0
Fair Value	203	215
Available-for-sale Securities [Abstract]
Cost or Amortized Cost	20,919	22,034
Gross Unrealized Appreciation	401	323
Gross Unrealized Depreciation	215	291
Fair Value	21,105	22,066
Collateralized Mortgage Obligations [Member]
Available-for-sale Securities [Abstract]
Cost or Amortized Cost	316,736	309,975
Gross Unrealized Appreciation	2,224	1,707
Gross Unrealized Depreciation	11,941	16,919
Fair Value	307,019	294,763
Asset-Backed Securities [Member]
Available-for-sale Securities [Abstract]
Cost or Amortized Cost	3,141	3,719
Gross Unrealized Appreciation	240	276
Gross Unrealized Depreciation	0	0
Fair Value	3,381	3,995
Equity Securities [Member]
Available-for-sale Securities [Abstract]
Cost or Amortized Cost	71,021	70,957
Gross Unrealized Appreciation	161,586	158,858
Gross Unrealized Depreciation	230	447
Fair Value	232,377	229,368
Common Stocks [Member] | Public Utilities [Member]
Available-for-sale Securities [Abstract]
Cost or Amortized Cost	7,231	7,231
Gross Unrealized Appreciation	10,231	9,068
Gross Unrealized Depreciation	0	27
Fair Value	17,462	16,272
Common Stocks [Member] | Energy [Member]
Available-for-sale Securities [Abstract]
Cost or Amortized Cost	5,094	5,094
Gross Unrealized Appreciation	9,562	9,269
Gross Unrealized Depreciation	0	0
Fair Value	14,656	14,363
Common Stocks [Member] | Industrials [Member]
Available-for-sale Securities [Abstract]
Cost or Amortized Cost	13,286	13,308
Gross Unrealized Appreciation	32,197	32,823
Gross Unrealized Depreciation	34	32
Fair Value	45,449	46,099
Common Stocks [Member] | Consumer Goods and Services [Member]
Available-for-sale Securities [Abstract]
Cost or Amortized Cost	10,363	10,363
Gross Unrealized Appreciation	10,933	10,895
Gross Unrealized Depreciation	3	0
Fair Value	21,293	21,258
Common Stocks [Member] | Health Care [Member]
Available-for-sale Securities [Abstract]
Cost or Amortized Cost	7,920	7,920
Gross Unrealized Appreciation	17,025	17,078
Gross Unrealized Depreciation	0	0
Fair Value	24,945	24,998
Common Stocks [Member] | Technology, Media and Telecommunications [Member]
Available-for-sale Securities [Abstract]
Cost or Amortized Cost	6,204	6,204
Gross Unrealized Appreciation	7,176	7,183
Gross Unrealized Depreciation	58	83
Fair Value	13,322	13,304
Common Stocks [Member] | Financial Services [Member]
Available-for-sale Securities [Abstract]
Cost or Amortized Cost	15,939	15,853
Gross Unrealized Appreciation	74,451	72,537
Gross Unrealized Depreciation	113	128
Fair Value	90,277	88,262
Nonredeemable Preferred Stocks [Member]
Available-for-sale Securities [Abstract]
Cost or Amortized Cost	4,984	4,984
Gross Unrealized Appreciation	11	5
Gross Unrealized Depreciation	22	177
Fair Value	$ 4,973	$ 4,812