Summary of Investments (Investments in Unrealized Loss Position) (Details) $ in Thousands	Jun. 30, 2016 USD ($) issue	Dec. 31, 2015 USD ($) issue
Number of Issues
Less than 12 months | issue	33	378
12 months or longer | issue	75	92
Fair Value
Less than 12 months	$ 58,519	$ 747,083
12 months or longer	81,279	140,558
Total	139,798	887,641
Gross Unrealized Depreciation
Less than 12 months	694	17,414
12 months or longer	4,699	10,677
Total	$ 5,393	$ 28,091
Fixed Maturities [Member]
Number of Issues
Less than 12 months | issue	25	350
12 months or longer | issue	50	79
Fair Value
Less than 12 months	$ 57,685	$ 743,274
12 months or longer	80,039	140,088
Total	137,724	883,362
Gross Unrealized Depreciation
Less than 12 months	609	16,962
12 months or longer	4,197	10,140
Total	$ 4,806	$ 27,102
U.S. Treasury [Member]
Number of Issues
Less than 12 months | issue		6
12 months or longer | issue		2
Fair Value
Less than 12 months		$ 6,408
12 months or longer		1,634
Total		8,042
Gross Unrealized Depreciation
Less than 12 months		26
12 months or longer		12
Total		$ 38
U.S. Government Agency [Member]
Number of Issues
Less than 12 months | issue		38
12 months or longer | issue		6
Fair Value
Less than 12 months		$ 104,621
12 months or longer		18,821
Total		123,442
Gross Unrealized Depreciation
Less than 12 months		1,771
12 months or longer		629
Total		$ 2,400
States, Municipalities and Political Subdivisions [Member] | General Obligations [Member] | Midwest [Member]
Number of Issues
Less than 12 months | issue		4
12 months or longer | issue		1
Fair Value
Less than 12 months		$ 2,417
12 months or longer		528
Total		2,945
Gross Unrealized Depreciation
Less than 12 months		12
12 months or longer		6
Total		$ 18
States, Municipalities and Political Subdivisions [Member] | General Obligations [Member] | South [Member]
Number of Issues
Less than 12 months | issue		3
12 months or longer | issue		8
Fair Value
Less than 12 months		$ 4,805
12 months or longer		3,743
Total		8,548
Gross Unrealized Depreciation
Less than 12 months		55
12 months or longer		79
Total		$ 134
States, Municipalities and Political Subdivisions [Member] | General Obligations [Member] | West [Member]
Number of Issues
Less than 12 months | issue		4
12 months or longer | issue		2
Fair Value
Less than 12 months		$ 8,927
12 months or longer		2,274
Total		11,201
Gross Unrealized Depreciation
Less than 12 months		23
12 months or longer		44
Total		$ 67
States, Municipalities and Political Subdivisions [Member] | Special Revenue [Member] | Midwest [Member]
Number of Issues
Less than 12 months | issue		0
12 months or longer | issue		1
Fair Value
Less than 12 months		$ 0
12 months or longer		2,494
Total		2,494
Gross Unrealized Depreciation
Less than 12 months		0
12 months or longer		30
Total		$ 30
States, Municipalities and Political Subdivisions [Member] | Special Revenue [Member] | Northeast [Member]
Number of Issues
Less than 12 months | issue		1
12 months or longer | issue		0
Fair Value
Less than 12 months		$ 4,755
12 months or longer		0
Total		4,755
Gross Unrealized Depreciation
Less than 12 months		212
12 months or longer		0
Total		$ 212
States, Municipalities and Political Subdivisions [Member] | Special Revenue [Member] | South [Member]
Number of Issues
Less than 12 months | issue	2	4
12 months or longer | issue	0	2
Fair Value
Less than 12 months	$ 5,524	$ 7,445
12 months or longer	0	1,851
Total	5,524	9,296
Gross Unrealized Depreciation
Less than 12 months	14	26
12 months or longer	0	1
Total	$ 14	$ 27
States, Municipalities and Political Subdivisions [Member] | Special Revenue [Member] | West [Member]
Number of Issues
Less than 12 months | issue		4
12 months or longer | issue		0
Fair Value
Less than 12 months		$ 6,851
12 months or longer		0
Total		6,851
Gross Unrealized Depreciation
Less than 12 months		44
12 months or longer		0
Total		$ 44
Foreign Bonds [Member]
Number of Issues
Less than 12 months | issue	0	9
12 months or longer | issue	5	2
Fair Value
Less than 12 months	$ 0	$ 16,991
12 months or longer	9,834	4,036
Total	9,834	21,027
Gross Unrealized Depreciation
Less than 12 months	0	1,289
12 months or longer	1,012	1,168
Total	$ 1,012	$ 2,457
Public Utilities [Member]
Number of Issues
Less than 12 months | issue	1	35
12 months or longer | issue	6	5
Fair Value
Less than 12 months	$ 852	$ 72,680
12 months or longer	6,540	2,840
Total	7,392	75,520
Gross Unrealized Depreciation
Less than 12 months	6	880
12 months or longer	275	371
Total	$ 281	$ 1,251
Corporate Bonds [Member] | Energy [Member]
Number of Issues
Less than 12 months | issue	7	29
12 months or longer | issue	6	4
Fair Value
Less than 12 months	$ 13,989	$ 61,496
12 months or longer	12,315	7,991
Total	26,304	69,487
Gross Unrealized Depreciation
Less than 12 months	145	3,286
12 months or longer	609	1,427
Total	$ 754	$ 4,713
Corporate Bonds [Member] | Industrials [Member]
Number of Issues
Less than 12 months | issue	2	38
12 months or longer | issue	5	3
Fair Value
Less than 12 months	$ 4,869	$ 78,588
12 months or longer	8,642	6,649
Total	13,511	85,237
Gross Unrealized Depreciation
Less than 12 months	246	3,631
12 months or longer	1,575	3,032
Total	$ 1,821	$ 6,663
Corporate Bonds [Member] | Consumer Goods and Services [Member]
Number of Issues
Less than 12 months | issue	0	24
12 months or longer | issue	4	4
Fair Value
Less than 12 months	$ 0	$ 64,661
12 months or longer	2,480	2,491
Total	2,480	67,152
Gross Unrealized Depreciation
Less than 12 months	0	770
12 months or longer	1	6
Total	$ 1	$ 776
Corporate Bonds [Member] | Health Care [Member]
Number of Issues
Less than 12 months | issue		18
12 months or longer | issue		2
Fair Value
Less than 12 months		$ 43,992
12 months or longer		3,737
Total		47,729
Gross Unrealized Depreciation
Less than 12 months		652
12 months or longer		139
Total		$ 791
Corporate Bonds [Member] | Technology, Media and Telecommunications [Member]
Number of Issues
Less than 12 months | issue	2	22
12 months or longer | issue	3	2
Fair Value
Less than 12 months	$ 4,837	$ 59,503
12 months or longer	10,158	8,940
Total	14,995	68,443
Gross Unrealized Depreciation
Less than 12 months	15	1,478
12 months or longer	423	525
Total	$ 438	$ 2,003
Corporate Bonds [Member] | Financial Services [Member]
Number of Issues
Less than 12 months | issue	1	49
12 months or longer | issue	1	0
Fair Value
Less than 12 months	$ 4,961	$ 92,814
12 months or longer	3,066	0
Total	8,027	92,814
Gross Unrealized Depreciation
Less than 12 months	36	1,143
12 months or longer	24	0
Total	$ 60	$ 1,143
Mortgage-Backed Securities [Member]
Number of Issues
Less than 12 months | issue	2	9
12 months or longer | issue	5	4
Fair Value
Less than 12 months	$ 5,279	$ 7,423
12 months or longer	1,267	183
Total	6,546	7,606
Gross Unrealized Depreciation
Less than 12 months	10	43
12 months or longer	11	8
Total	$ 21	$ 51
Government National Mortgage Association [Member]
Number of Issues
Less than 12 months | issue	2	17
12 months or longer | issue	8	14
Fair Value
Less than 12 months	$ 5,142	$ 29,769
12 months or longer	14,372	40,027
Total	19,514	69,796
Gross Unrealized Depreciation
Less than 12 months	28	437
12 months or longer	145	1,548
Total	$ 173	$ 1,985
Federal Home Loan Mortgage Corporation [Member]
Number of Issues
Less than 12 months | issue	2	20
12 months or longer | issue	3	6
Fair Value
Less than 12 months	$ 6,249	$ 35,343
12 months or longer	6,398	19,887
Total	12,647	55,230
Gross Unrealized Depreciation
Less than 12 months	3	644
12 months or longer	46	698
Total	$ 49	$ 1,342
Federal National Mortgage Association [Member]
Number of Issues
Less than 12 months | issue	3	15
12 months or longer | issue	4	11
Fair Value
Less than 12 months	$ 3,287	$ 32,800
12 months or longer	4,967	11,962
Total	8,254	44,762
Gross Unrealized Depreciation
Less than 12 months	9	524
12 months or longer	76	417
Total	$ 85	$ 941
Asset-backed Securities [Member]
Number of Issues
Less than 12 months | issue	1	1
12 months or longer | issue	0	0
Fair Value
Less than 12 months	$ 2,696	$ 985
12 months or longer	0	0
Total	2,696	985
Gross Unrealized Depreciation
Less than 12 months	97	16
12 months or longer	0	0
Total	$ 97	$ 16
Equity Securities [Member]
Number of Issues
Less than 12 months | issue	8	28
12 months or longer | issue	25	13
Fair Value
Less than 12 months	$ 834	$ 3,809
12 months or longer	1,240	470
Total	2,074	4,279
Gross Unrealized Depreciation
Less than 12 months	85	452
12 months or longer	502	537
Total	$ 587	$ 989
Common Stocks [Member] | Public Utilities [Member]
Number of Issues
Less than 12 months | issue	0	0
12 months or longer | issue	3	3
Fair Value
Less than 12 months	$ 0	$ 0
12 months or longer	146	115
Total	146	115
Gross Unrealized Depreciation
Less than 12 months	0	0
12 months or longer	161	193
Total	$ 161	$ 193
Common Stocks [Member] | Energy [Member]
Number of Issues
Less than 12 months | issue	1	10
12 months or longer | issue	1	0
Fair Value
Less than 12 months	$ 165	$ 2,868
12 months or longer	166	0
Total	331	2,868
Gross Unrealized Depreciation
Less than 12 months	26	266
12 months or longer	20	0
Total	$ 46	$ 266
Common Stocks [Member] | Industrials [Member]
Number of Issues
Less than 12 months | issue	0	3
12 months or longer | issue	6	5
Fair Value
Less than 12 months	$ 0	$ 177
12 months or longer	256	193
Total	256	370
Gross Unrealized Depreciation
Less than 12 months	0	44
12 months or longer	207	269
Total	$ 207	$ 313
Common Stocks [Member] | Consumer Goods and Services [Member]
Number of Issues
Less than 12 months | issue	4	0
12 months or longer | issue	2	2
Fair Value
Less than 12 months	$ 306	$ 0
12 months or longer	12	14
Total	318	14
Gross Unrealized Depreciation
Less than 12 months	40	0
12 months or longer	5	3
Total	$ 45	$ 3
Common Stocks [Member] | Technology, Media and Telecommunications [Member]
Number of Issues
Less than 12 months | issue	0	9
12 months or longer | issue	11	2
Fair Value
Less than 12 months	$ 0	$ 438
12 months or longer	500	12
Total	500	450
Gross Unrealized Depreciation
Less than 12 months	0	91
12 months or longer	55	14
Total	$ 55	$ 105
Common Stocks [Member] | Financial Services [Member]
Number of Issues
Less than 12 months | issue	3	6
12 months or longer | issue	2	1
Fair Value
Less than 12 months	$ 363	$ 326
12 months or longer	160	136
Total	523	462
Gross Unrealized Depreciation
Less than 12 months	19	51
12 months or longer	54	58
Total	$ 73	$ 109