Summary of Investments (Investments in Unrealized Loss Position) (Details) $ in Thousands	Mar. 31, 2016 USD ($) issue	Dec. 31, 2015 USD ($) issue
AVAILABLE-FOR-SALE
Less than 12 months, Number of Issues | issue	107	378
Less than 12 months, Fair Value	$ 186,804	$ 747,083
Less than 12 months, Gross Unrealized Depreciation	$ 4,989	$ 17,414
12 months or longer, Number of Issues | issue	82	92
12 months or longer, Fair Value	$ 116,749	$ 140,558
12 months or longer, Gross Unrealized Depreciation	7,545	10,677
Total, Fair Value	303,553	887,641
Total, Gross Unrealized Depreciation	$ 12,534	$ 28,091
Fixed Maturities [Member]
AVAILABLE-FOR-SALE
Less than 12 months, Number of Issues | issue	82	350
Less than 12 months, Fair Value	$ 183,940	$ 743,274
Less than 12 months, Gross Unrealized Depreciation	$ 4,760	$ 16,962
12 months or longer, Number of Issues | issue	65	79
12 months or longer, Fair Value	$ 116,197	$ 140,088
12 months or longer, Gross Unrealized Depreciation	7,048	10,140
Total, Fair Value	300,137	883,362
Total, Gross Unrealized Depreciation	$ 11,808	$ 27,102
U.S. Treasury [Member]
AVAILABLE-FOR-SALE
Less than 12 months, Number of Issues | issue	0	6
Less than 12 months, Fair Value	$ 0	$ 6,408
Less than 12 months, Gross Unrealized Depreciation	$ 0	$ 26
12 months or longer, Number of Issues | issue	2	2
12 months or longer, Fair Value	$ 1,637	$ 1,634
12 months or longer, Gross Unrealized Depreciation	3	12
Total, Fair Value	1,637	8,042
Total, Gross Unrealized Depreciation	$ 3	$ 38
U.S. Government Agency [Member]
AVAILABLE-FOR-SALE
Less than 12 months, Number of Issues | issue	7	38
Less than 12 months, Fair Value	$ 18,173	$ 104,621
Less than 12 months, Gross Unrealized Depreciation	$ 25	$ 1,771
12 months or longer, Number of Issues | issue	1	6
12 months or longer, Fair Value	$ 2,995	$ 18,821
12 months or longer, Gross Unrealized Depreciation	3	629
Total, Fair Value	21,168	123,442
Total, Gross Unrealized Depreciation	$ 28	$ 2,400
States, Municipalities and Political Subdivisions [Member] | General Obligations [Member] | Midwest [Member]
AVAILABLE-FOR-SALE
Less than 12 months, Number of Issues | issue	3	4
Less than 12 months, Fair Value	$ 9,619	$ 2,417
Less than 12 months, Gross Unrealized Depreciation	$ 14	$ 12
12 months or longer, Number of Issues | issue	0	1
12 months or longer, Fair Value	$ 0	$ 528
12 months or longer, Gross Unrealized Depreciation	0	6
Total, Fair Value	9,619	2,945
Total, Gross Unrealized Depreciation	$ 14	$ 18
States, Municipalities and Political Subdivisions [Member] | General Obligations [Member] | South [Member]
AVAILABLE-FOR-SALE
Less than 12 months, Number of Issues | issue		3
Less than 12 months, Fair Value		$ 4,805
Less than 12 months, Gross Unrealized Depreciation		$ 55
12 months or longer, Number of Issues | issue		8
12 months or longer, Fair Value		$ 3,743
12 months or longer, Gross Unrealized Depreciation		79
Total, Fair Value		8,548
Total, Gross Unrealized Depreciation		$ 134
States, Municipalities and Political Subdivisions [Member] | General Obligations [Member] | West [Member]
AVAILABLE-FOR-SALE
Less than 12 months, Number of Issues | issue	1	4
Less than 12 months, Fair Value	$ 3,136	$ 8,927
Less than 12 months, Gross Unrealized Depreciation	$ 37	$ 23
12 months or longer, Number of Issues | issue	2	2
12 months or longer, Fair Value	$ 2,301	$ 2,274
12 months or longer, Gross Unrealized Depreciation	12	44
Total, Fair Value	5,437	11,201
Total, Gross Unrealized Depreciation	$ 49	$ 67
States, Municipalities and Political Subdivisions [Member] | Special Revenue [Member] | Midwest [Member]
AVAILABLE-FOR-SALE
Less than 12 months, Number of Issues | issue		0
Less than 12 months, Fair Value		$ 0
Less than 12 months, Gross Unrealized Depreciation		$ 0
12 months or longer, Number of Issues | issue		1
12 months or longer, Fair Value		$ 2,494
12 months or longer, Gross Unrealized Depreciation		30
Total, Fair Value		2,494
Total, Gross Unrealized Depreciation		$ 30
States, Municipalities and Political Subdivisions [Member] | Special Revenue [Member] | Northeast [Member]
AVAILABLE-FOR-SALE
Less than 12 months, Number of Issues | issue	1	1
Less than 12 months, Fair Value	$ 1,037	$ 4,755
Less than 12 months, Gross Unrealized Depreciation	$ 4	$ 212
12 months or longer, Number of Issues | issue	0	0
12 months or longer, Fair Value	$ 0	$ 0
12 months or longer, Gross Unrealized Depreciation	0	0
Total, Fair Value	1,037	4,755
Total, Gross Unrealized Depreciation	$ 4	$ 212
States, Municipalities and Political Subdivisions [Member] | Special Revenue [Member] | South [Member]
AVAILABLE-FOR-SALE
Less than 12 months, Number of Issues | issue	3	4
Less than 12 months, Fair Value	$ 4,149	$ 7,445
Less than 12 months, Gross Unrealized Depreciation	$ 7	$ 26
12 months or longer, Number of Issues | issue	0	2
12 months or longer, Fair Value	$ 0	$ 1,851
12 months or longer, Gross Unrealized Depreciation	0	1
Total, Fair Value	4,149	9,296
Total, Gross Unrealized Depreciation	$ 7	$ 27
States, Municipalities and Political Subdivisions [Member] | Special Revenue [Member] | West [Member]
AVAILABLE-FOR-SALE
Less than 12 months, Number of Issues | issue	0	4
Less than 12 months, Fair Value	$ 0	$ 6,851
Less than 12 months, Gross Unrealized Depreciation	$ 0	$ 44
12 months or longer, Number of Issues | issue	1	0
12 months or longer, Fair Value	$ 719	$ 0
12 months or longer, Gross Unrealized Depreciation	2	0
Total, Fair Value	719	6,851
Total, Gross Unrealized Depreciation	$ 2	$ 44
Foreign Bonds [Member]
AVAILABLE-FOR-SALE
Less than 12 months, Number of Issues | issue	7	9
Less than 12 months, Fair Value	$ 11,277	$ 16,991
Less than 12 months, Gross Unrealized Depreciation	$ 534	$ 1,289
12 months or longer, Number of Issues | issue	2	2
12 months or longer, Fair Value	$ 3,804	$ 4,036
12 months or longer, Gross Unrealized Depreciation	1,391	1,168
Total, Fair Value	15,081	21,027
Total, Gross Unrealized Depreciation	$ 1,925	$ 2,457
Public Utilities [Member]
AVAILABLE-FOR-SALE
Less than 12 months, Number of Issues | issue	4	35
Less than 12 months, Fair Value	$ 8,231	$ 72,680
Less than 12 months, Gross Unrealized Depreciation	$ 394	$ 880
12 months or longer, Number of Issues | issue	6	5
12 months or longer, Fair Value	$ 5,997	$ 2,840
12 months or longer, Gross Unrealized Depreciation	432	371
Total, Fair Value	14,228	75,520
Total, Gross Unrealized Depreciation	$ 826	$ 1,251
Corporate Bonds [Member] | Energy [Member]
AVAILABLE-FOR-SALE
Less than 12 months, Number of Issues | issue	20	29
Less than 12 months, Fair Value	$ 44,540	$ 61,496
Less than 12 months, Gross Unrealized Depreciation	$ 2,328	$ 3,286
12 months or longer, Number of Issues | issue	5	4
12 months or longer, Fair Value	$ 10,764	$ 7,991
12 months or longer, Gross Unrealized Depreciation	1,094	1,427
Total, Fair Value	55,304	69,487
Total, Gross Unrealized Depreciation	$ 3,422	$ 4,713
Corporate Bonds [Member] | Industrials [Member]
AVAILABLE-FOR-SALE
Less than 12 months, Number of Issues | issue	8	38
Less than 12 months, Fair Value	$ 16,891	$ 78,588
Less than 12 months, Gross Unrealized Depreciation	$ 618	$ 3,631
12 months or longer, Number of Issues | issue	8	3
12 months or longer, Fair Value	$ 15,276	$ 6,649
12 months or longer, Gross Unrealized Depreciation	2,658	3,032
Total, Fair Value	32,167	85,237
Total, Gross Unrealized Depreciation	$ 3,276	$ 6,663
Corporate Bonds [Member] | Consumer Goods and Services [Member]
AVAILABLE-FOR-SALE
Less than 12 months, Number of Issues | issue	0	24
Less than 12 months, Fair Value	$ 0	$ 64,661
Less than 12 months, Gross Unrealized Depreciation	$ 0	$ 770
12 months or longer, Number of Issues | issue	4	4
12 months or longer, Fair Value	$ 2,486	$ 2,491
12 months or longer, Gross Unrealized Depreciation	3	6
Total, Fair Value	2,486	67,152
Total, Gross Unrealized Depreciation	$ 3	$ 776
Corporate Bonds [Member] | Health Care [Member]
AVAILABLE-FOR-SALE
Less than 12 months, Number of Issues | issue	0	18
Less than 12 months, Fair Value	$ 0	$ 43,992
Less than 12 months, Gross Unrealized Depreciation	$ 0	$ 652
12 months or longer, Number of Issues | issue	2	2
12 months or longer, Fair Value	$ 2,732	$ 3,737
12 months or longer, Gross Unrealized Depreciation	43	139
Total, Fair Value	2,732	47,729
Total, Gross Unrealized Depreciation	$ 43	$ 791
Corporate Bonds [Member] | Technology, Media and Telecommunications [Member]
AVAILABLE-FOR-SALE
Less than 12 months, Number of Issues | issue	9	22
Less than 12 months, Fair Value	$ 26,290	$ 59,503
Less than 12 months, Gross Unrealized Depreciation	$ 365	$ 1,478
12 months or longer, Number of Issues | issue	4	2
12 months or longer, Fair Value	$ 15,132	$ 8,940
12 months or longer, Gross Unrealized Depreciation	705	525
Total, Fair Value	41,422	68,443
Total, Gross Unrealized Depreciation	$ 1,070	$ 2,003
Corporate Bonds [Member] | Financial Services [Member]
AVAILABLE-FOR-SALE
Less than 12 months, Number of Issues | issue	8	49
Less than 12 months, Fair Value	$ 17,662	$ 92,814
Less than 12 months, Gross Unrealized Depreciation	$ 160	$ 1,143
12 months or longer, Number of Issues | issue	3	0
12 months or longer, Fair Value	$ 6,130	$ 0
12 months or longer, Gross Unrealized Depreciation	68	0
Total, Fair Value	23,792	92,814
Total, Gross Unrealized Depreciation	$ 228	$ 1,143
Mortgage-Backed Securities [Member]
AVAILABLE-FOR-SALE
Less than 12 months, Number of Issues | issue	0	9
Less than 12 months, Fair Value	$ 0	$ 7,423
Less than 12 months, Gross Unrealized Depreciation	$ 0	$ 43
12 months or longer, Number of Issues | issue	4	4
12 months or longer, Fair Value	$ 1,379	$ 183
12 months or longer, Gross Unrealized Depreciation	17	8
Total, Fair Value	1,379	7,606
Total, Gross Unrealized Depreciation	$ 17	$ 51
Government National Mortgage Association [Member]
AVAILABLE-FOR-SALE
Less than 12 months, Number of Issues | issue	5	17
Less than 12 months, Fair Value	$ 7,888	$ 29,769
Less than 12 months, Gross Unrealized Depreciation	$ 22	$ 437
12 months or longer, Number of Issues | issue	12	14
12 months or longer, Fair Value	$ 26,988	$ 40,027
12 months or longer, Gross Unrealized Depreciation	381	1,548
Total, Fair Value	34,876	69,796
Total, Gross Unrealized Depreciation	$ 403	$ 1,985
Federal Home Loan Mortgage Corporation [Member]
AVAILABLE-FOR-SALE
Less than 12 months, Number of Issues | issue	1	20
Less than 12 months, Fair Value	$ 6,970	$ 35,343
Less than 12 months, Gross Unrealized Depreciation	$ 18	$ 644
12 months or longer, Number of Issues | issue	5	6
12 months or longer, Fair Value	$ 12,692	$ 19,887
12 months or longer, Gross Unrealized Depreciation	131	698
Total, Fair Value	19,662	55,230
Total, Gross Unrealized Depreciation	$ 149	$ 1,342
Federal National Mortgage Association [Member]
AVAILABLE-FOR-SALE
Less than 12 months, Number of Issues | issue	4	15
Less than 12 months, Fair Value	$ 5,503	$ 32,800
Less than 12 months, Gross Unrealized Depreciation	$ 22	$ 524
12 months or longer, Number of Issues | issue	4	11
12 months or longer, Fair Value	$ 5,165	$ 11,962
12 months or longer, Gross Unrealized Depreciation	105	417
Total, Fair Value	10,668	44,762
Total, Gross Unrealized Depreciation	$ 127	$ 941
Asset-backed Securities [Member]
AVAILABLE-FOR-SALE
Less than 12 months, Number of Issues | issue	1	1
Less than 12 months, Fair Value	$ 2,574	$ 985
Less than 12 months, Gross Unrealized Depreciation	$ 212	$ 16
12 months or longer, Number of Issues | issue	0	0
12 months or longer, Fair Value	$ 0	$ 0
12 months or longer, Gross Unrealized Depreciation	0	0
Total, Fair Value	2,574	985
Total, Gross Unrealized Depreciation	$ 212	$ 16
Equity Securities [Member]
AVAILABLE-FOR-SALE
Less than 12 months, Number of Issues | issue	25	28
Less than 12 months, Fair Value	$ 2,864	$ 3,809
Less than 12 months, Gross Unrealized Depreciation	$ 229	$ 452
12 months or longer, Number of Issues | issue	17	13
12 months or longer, Fair Value	$ 552	$ 470
12 months or longer, Gross Unrealized Depreciation	497	537
Total, Fair Value	3,416	4,279
Total, Gross Unrealized Depreciation	$ 726	$ 989
Common Stocks [Member] | Public Utilities [Member]
AVAILABLE-FOR-SALE
Less than 12 months, Number of Issues | issue	0	0
Less than 12 months, Fair Value	$ 0	$ 0
Less than 12 months, Gross Unrealized Depreciation	$ 0	$ 0
12 months or longer, Number of Issues | issue	3	3
12 months or longer, Fair Value	$ 127	$ 115
12 months or longer, Gross Unrealized Depreciation	181	193
Total, Fair Value	127	115
Total, Gross Unrealized Depreciation	$ 181	$ 193
Common Stocks [Member] | Energy [Member]
AVAILABLE-FOR-SALE
Less than 12 months, Number of Issues | issue	8	10
Less than 12 months, Fair Value	$ 1,935	$ 2,868
Less than 12 months, Gross Unrealized Depreciation	$ 158	$ 266
12 months or longer, Number of Issues | issue	0	0
12 months or longer, Fair Value	$ 0	$ 0
12 months or longer, Gross Unrealized Depreciation	0	0
Total, Fair Value	1,935	2,868
Total, Gross Unrealized Depreciation	$ 158	$ 266
Common Stocks [Member] | Industrials [Member]
AVAILABLE-FOR-SALE
Less than 12 months, Number of Issues | issue	2	3
Less than 12 months, Fair Value	$ 1	$ 177
Less than 12 months, Gross Unrealized Depreciation	$ 1	$ 44
12 months or longer, Number of Issues | issue	5	5
12 months or longer, Fair Value	$ 231	$ 193
12 months or longer, Gross Unrealized Depreciation	231	269
Total, Fair Value	232	370
Total, Gross Unrealized Depreciation	$ 232	$ 313
Common Stocks [Member] | Consumer Goods and Services [Member]
AVAILABLE-FOR-SALE
Less than 12 months, Number of Issues | issue	2	0
Less than 12 months, Fair Value	$ 32	$ 0
Less than 12 months, Gross Unrealized Depreciation	$ 1	$ 0
12 months or longer, Number of Issues | issue	2	2
12 months or longer, Fair Value	$ 13	$ 14
12 months or longer, Gross Unrealized Depreciation	4	3
Total, Fair Value	45	14
Total, Gross Unrealized Depreciation	$ 5	$ 3
Common Stocks [Member] | Technology, Media and Telecommunications [Member]
AVAILABLE-FOR-SALE
Less than 12 months, Number of Issues | issue	7	9
Less than 12 months, Fair Value	$ 488	$ 438
Less than 12 months, Gross Unrealized Depreciation	$ 40	$ 91
12 months or longer, Number of Issues | issue	5	2
12 months or longer, Fair Value	$ 31	$ 12
12 months or longer, Gross Unrealized Depreciation	17	14
Total, Fair Value	519	450
Total, Gross Unrealized Depreciation	$ 57	$ 105
Common Stocks [Member] | Financial Services [Member]
AVAILABLE-FOR-SALE
Less than 12 months, Number of Issues | issue	6	6
Less than 12 months, Fair Value	$ 408	$ 326
Less than 12 months, Gross Unrealized Depreciation	$ 29	$ 51
12 months or longer, Number of Issues | issue	2	1
12 months or longer, Fair Value	$ 150	$ 136
12 months or longer, Gross Unrealized Depreciation	64	58
Total, Fair Value	558	462
Total, Gross Unrealized Depreciation	$ 93	$ 109