Summary of Investments (Investments in Unrealized Loss Position) (Details) $ in Thousands	Jun. 30, 2015 USD ($) issue	Dec. 31, 2014 USD ($) issue
Available-for-sale
Less than 12 months, Number of Issues | issue	457	117
Less than 12 months, Fair Value	$ 801,073	$ 221,670
Less than 12 months, Gross Unrealized Depreciation	$ 15,338	$ 2,660
12 months or longer, Number of Issues | issue	86	195
12 months or longer, Fair Value	$ 140,520	$ 335,951
12 months or longer, Gross Unrealized Depreciation	7,853	11,268
Total, Fair Value	941,593	557,621
Total, Gross Unrealized Depreciation	$ 23,191	$ 13,928
Fixed Maturities [Member]
Available-for-sale
Less than 12 months, Number of Issues | issue	436	105
Less than 12 months, Fair Value	$ 799,885	$ 220,309
Less than 12 months, Gross Unrealized Depreciation	$ 15,121	$ 2,209
12 months or longer, Number of Issues | issue	78	185
12 months or longer, Fair Value	$ 140,193	$ 334,960
12 months or longer, Gross Unrealized Depreciation	7,724	11,160
Total, Fair Value	940,078	555,269
Total, Gross Unrealized Depreciation	$ 22,845	$ 13,369
U.S. Treasury [Member]
Available-for-sale
Less than 12 months, Number of Issues | issue	2	4
Less than 12 months, Fair Value	$ 3,415	$ 2,343
Less than 12 months, Gross Unrealized Depreciation	$ 2	$ 6
12 months or longer, Number of Issues | issue	2	4
12 months or longer, Fair Value	$ 1,656	$ 5,069
12 months or longer, Gross Unrealized Depreciation	5	46
Total, Fair Value	5,071	7,412
Total, Gross Unrealized Depreciation	$ 7	$ 52
U.S. Government Agency [Member]
Available-for-sale
Less than 12 months, Number of Issues | issue	43	11
Less than 12 months, Fair Value	$ 124,251	$ 41,064
Less than 12 months, Gross Unrealized Depreciation	$ 2,360	$ 70
12 months or longer, Number of Issues | issue	7	35
12 months or longer, Fair Value	$ 21,534	$ 95,198
12 months or longer, Gross Unrealized Depreciation	915	2,352
Total, Fair Value	145,785	136,262
Total, Gross Unrealized Depreciation	$ 3,275	$ 2,422
States, Municipalities and Political Subdivisions [Member] | General Obligations [Member] | Midwest [Member]
Available-for-sale
Less than 12 months, Number of Issues | issue	28	1
Less than 12 months, Fair Value	$ 27,667	$ 3,650
Less than 12 months, Gross Unrealized Depreciation	$ 684	$ 74
12 months or longer, Number of Issues | issue	0	14
12 months or longer, Fair Value	$ 0	$ 9,856
12 months or longer, Gross Unrealized Depreciation	0	96
Total, Fair Value	27,667	13,506
Total, Gross Unrealized Depreciation	$ 684	$ 170
States, Municipalities and Political Subdivisions [Member] | General Obligations [Member] | Northeast [Member]
Available-for-sale
Less than 12 months, Number of Issues | issue	15	0
Less than 12 months, Fair Value	$ 21,479	$ 0
Less than 12 months, Gross Unrealized Depreciation	$ 293	$ 0
12 months or longer, Number of Issues | issue	0	9
12 months or longer, Fair Value	$ 0	$ 7,377
12 months or longer, Gross Unrealized Depreciation	0	50
Total, Fair Value	21,479	7,377
Total, Gross Unrealized Depreciation	$ 293	$ 50
States, Municipalities and Political Subdivisions [Member] | General Obligations [Member] | South [Member]
Available-for-sale
Less than 12 months, Number of Issues | issue	25	1
Less than 12 months, Fair Value	$ 33,704	$ 3,085
Less than 12 months, Gross Unrealized Depreciation	$ 769	$ 58
12 months or longer, Number of Issues | issue	12	19
12 months or longer, Fair Value	$ 6,429	$ 13,475
12 months or longer, Gross Unrealized Depreciation	308	230
Total, Fair Value	40,133	16,560
Total, Gross Unrealized Depreciation	$ 1,077	$ 288
States, Municipalities and Political Subdivisions [Member] | General Obligations [Member] | West [Member]
Available-for-sale
Less than 12 months, Number of Issues | issue	25	1
Less than 12 months, Fair Value	$ 36,157	$ 1,023
Less than 12 months, Gross Unrealized Depreciation	$ 789	$ 1
12 months or longer, Number of Issues | issue	0	5
12 months or longer, Fair Value	$ 0	$ 2,700
12 months or longer, Gross Unrealized Depreciation	0	18
Total, Fair Value	36,157	3,723
Total, Gross Unrealized Depreciation	$ 789	$ 19
States, Municipalities and Political Subdivisions [Member] | Special Revenue [Member] | Midwest [Member]
Available-for-sale
Less than 12 months, Number of Issues | issue	36	9
Less than 12 months, Fair Value	$ 39,349	$ 10,219
Less than 12 months, Gross Unrealized Depreciation	$ 823	$ 41
12 months or longer, Number of Issues | issue	1	8
12 months or longer, Fair Value	$ 2,443	$ 11,631
12 months or longer, Gross Unrealized Depreciation	88	105
Total, Fair Value	41,792	21,850
Total, Gross Unrealized Depreciation	$ 911	$ 146
States, Municipalities and Political Subdivisions [Member] | Special Revenue [Member] | Northeast [Member]
Available-for-sale
Less than 12 months, Number of Issues | issue	3
Less than 12 months, Fair Value	$ 7,540
Less than 12 months, Gross Unrealized Depreciation	$ 242
12 months or longer, Number of Issues | issue	0
12 months or longer, Fair Value	$ 0
12 months or longer, Gross Unrealized Depreciation	0
Total, Fair Value	7,540
Total, Gross Unrealized Depreciation	$ 242
States, Municipalities and Political Subdivisions [Member] | Special Revenue [Member] | South [Member]
Available-for-sale
Less than 12 months, Number of Issues | issue	18	6
Less than 12 months, Fair Value	$ 25,118	$ 12,882
Less than 12 months, Gross Unrealized Depreciation	$ 495	$ 11
12 months or longer, Number of Issues | issue	2	3
12 months or longer, Fair Value	$ 1,798	$ 2,137
12 months or longer, Gross Unrealized Depreciation	61	52
Total, Fair Value	26,916	15,019
Total, Gross Unrealized Depreciation	$ 556	$ 63
States, Municipalities and Political Subdivisions [Member] | Special Revenue [Member] | West [Member]
Available-for-sale
Less than 12 months, Number of Issues | issue	24	0
Less than 12 months, Fair Value	$ 23,266	$ 0
Less than 12 months, Gross Unrealized Depreciation	$ 388	$ 0
12 months or longer, Number of Issues | issue	0	4
12 months or longer, Fair Value	$ 0	$ 3,671
12 months or longer, Gross Unrealized Depreciation	0	6
Total, Fair Value	23,266	3,671
Total, Gross Unrealized Depreciation	$ 388	$ 6
Foreign Bonds [Member]
Available-for-sale
Less than 12 months, Number of Issues | issue	5	6
Less than 12 months, Fair Value	$ 12,206	$ 17,158
Less than 12 months, Gross Unrealized Depreciation	$ 167	$ 446
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	12,206	17,158
Total, Gross Unrealized Depreciation	$ 167	$ 446
Public Utilities [Member]
Available-for-sale
Less than 12 months, Number of Issues | issue	28	10
Less than 12 months, Fair Value	$ 52,883	$ 21,839
Less than 12 months, Gross Unrealized Depreciation	$ 824	$ 194
12 months or longer, Number of Issues | issue	3	4
12 months or longer, Fair Value	$ 2,121	$ 3,611
12 months or longer, Gross Unrealized Depreciation	112	294
Total, Fair Value	55,004	25,450
Total, Gross Unrealized Depreciation	$ 936	$ 488
Corporate Bonds [Member] | Energy [Member]
Available-for-sale
Less than 12 months, Number of Issues | issue	8	8
Less than 12 months, Fair Value	$ 22,313	$ 17,416
Less than 12 months, Gross Unrealized Depreciation	$ 341	$ 420
12 months or longer, Number of Issues | issue	3	3
12 months or longer, Fair Value	$ 7,021	$ 7,061
12 months or longer, Gross Unrealized Depreciation	380	373
Total, Fair Value	29,334	24,477
Total, Gross Unrealized Depreciation	$ 721	$ 793
Corporate Bonds [Member] | Industrials [Member]
Available-for-sale
Less than 12 months, Number of Issues | issue	29	8
Less than 12 months, Fair Value	$ 60,462	$ 17,103
Less than 12 months, Gross Unrealized Depreciation	$ 1,189	$ 362
12 months or longer, Number of Issues | issue	2	3
12 months or longer, Fair Value	$ 6,197	$ 9,592
12 months or longer, Gross Unrealized Depreciation	1,833	1,792
Total, Fair Value	66,659	26,695
Total, Gross Unrealized Depreciation	$ 3,022	$ 2,154
Corporate Bonds [Member] | Consumer Goods and Services [Member]
Available-for-sale
Less than 12 months, Number of Issues | issue	17	11
Less than 12 months, Fair Value	$ 44,538	$ 28,344
Less than 12 months, Gross Unrealized Depreciation	$ 655	$ 258
12 months or longer, Number of Issues | issue	4	7
12 months or longer, Fair Value	$ 2,505	$ 10,064
12 months or longer, Gross Unrealized Depreciation	9	66
Total, Fair Value	47,043	38,408
Total, Gross Unrealized Depreciation	$ 664	$ 324
Corporate Bonds [Member] | Health Care [Member]
Available-for-sale
Less than 12 months, Number of Issues | issue	13	3
Less than 12 months, Fair Value	$ 34,156	$ 8,244
Less than 12 months, Gross Unrealized Depreciation	$ 849	$ 36
12 months or longer, Number of Issues | issue	2	3
12 months or longer, Fair Value	$ 3,790	$ 7,104
12 months or longer, Gross Unrealized Depreciation	115	174
Total, Fair Value	37,946	15,348
Total, Gross Unrealized Depreciation	$ 964	$ 210
Corporate Bonds [Member] | Technology, Media and Telecommunications [Member]
Available-for-sale
Less than 12 months, Number of Issues | issue	21	4
Less than 12 months, Fair Value	$ 60,661	$ 8,860
Less than 12 months, Gross Unrealized Depreciation	$ 996	$ 68
12 months or longer, Number of Issues | issue	2	4
12 months or longer, Fair Value	$ 9,162	$ 15,742
12 months or longer, Gross Unrealized Depreciation	343	731
Total, Fair Value	69,823	24,602
Total, Gross Unrealized Depreciation	$ 1,339	$ 799
Corporate Bonds [Member] | Financial Services [Member]
Available-for-sale
Less than 12 months, Number of Issues | issue	29	3
Less than 12 months, Fair Value	$ 58,901	$ 5,908
Less than 12 months, Gross Unrealized Depreciation	$ 1,069	$ 31
12 months or longer, Number of Issues | issue	0	2
12 months or longer, Fair Value	$ 0	$ 6,131
12 months or longer, Gross Unrealized Depreciation	0	56
Total, Fair Value	58,901	12,039
Total, Gross Unrealized Depreciation	$ 1,069	$ 87
Mortgage-Backed Securities [Member]
Available-for-sale
Less than 12 months, Number of Issues | issue	8	9
Less than 12 months, Fair Value	$ 4,748	$ 425
Less than 12 months, Gross Unrealized Depreciation	$ 59	$ 21
12 months or longer, Number of Issues | issue	1	2
12 months or longer, Fair Value	$ 80	$ 1,991
12 months or longer, Gross Unrealized Depreciation	1	25
Total, Fair Value	4,828	2,416
Total, Gross Unrealized Depreciation	$ 60	$ 46
Collateralized Mortgage Obligations [Member]
Available-for-sale
Less than 12 months, Number of Issues | issue	58	10
Less than 12 months, Fair Value	$ 106,085	$ 20,746
Less than 12 months, Gross Unrealized Depreciation	$ 2,113	$ 112
12 months or longer, Number of Issues | issue	37	56
12 months or longer, Fair Value	$ 75,457	$ 122,550
12 months or longer, Gross Unrealized Depreciation	3,554	4,694
Total, Fair Value	181,542	143,296
Total, Gross Unrealized Depreciation	$ 5,667	$ 4,806
Asset-backed Securities [Member]
Available-for-sale
Less than 12 months, Number of Issues | issue	1
Less than 12 months, Fair Value	$ 986
Less than 12 months, Gross Unrealized Depreciation	$ 14
12 months or longer, Number of Issues | issue	0
12 months or longer, Fair Value	$ 0
12 months or longer, Gross Unrealized Depreciation	0
Total, Fair Value	986
Total, Gross Unrealized Depreciation	$ 14
Equity Securities [Member]
Available-for-sale
Less than 12 months, Number of Issues | issue	21	12
Less than 12 months, Fair Value	$ 1,188	$ 1,361
Less than 12 months, Gross Unrealized Depreciation	$ 217	$ 451
12 months or longer, Number of Issues | issue	8	10
12 months or longer, Fair Value	$ 327	$ 991
12 months or longer, Gross Unrealized Depreciation	129	108
Total, Fair Value	1,515	2,352
Total, Gross Unrealized Depreciation	$ 346	$ 559
Common Stocks [Member] | Public Utilities [Member]
Available-for-sale
Less than 12 months, Number of Issues | issue	0	3
Less than 12 months, Fair Value	$ 0	$ 263
Less than 12 months, Gross Unrealized Depreciation	$ 0	$ 44
12 months or longer, Number of Issues | issue	3	0
12 months or longer, Fair Value	$ 223	$ 0
12 months or longer, Gross Unrealized Depreciation	84	0
Total, Fair Value	223	263
Total, Gross Unrealized Depreciation	$ 84	$ 44
Common Stocks [Member] | Energy [Member]
Available-for-sale
Less than 12 months, Number of Issues | issue	1
Less than 12 months, Fair Value	$ 171
Less than 12 months, Gross Unrealized Depreciation	$ 15
12 months or longer, Number of Issues | issue	0
12 months or longer, Fair Value	$ 0
12 months or longer, Gross Unrealized Depreciation	0
Total, Fair Value	171
Total, Gross Unrealized Depreciation	$ 15
Common Stocks [Member] | Industrials [Member]
Available-for-sale
Less than 12 months, Number of Issues | issue	4	3
Less than 12 months, Fair Value	$ 229	$ 280
Less than 12 months, Gross Unrealized Depreciation	$ 121	$ 70
12 months or longer, Number of Issues | issue	2	2
12 months or longer, Fair Value	$ 80	$ 58
12 months or longer, Gross Unrealized Depreciation	32	54
Total, Fair Value	309	338
Total, Gross Unrealized Depreciation	$ 153	$ 124
Common Stocks [Member] | Consumer Goods and Services [Member]
Available-for-sale
Less than 12 months, Number of Issues | issue	0	1
Less than 12 months, Fair Value	$ 0	$ 129
Less than 12 months, Gross Unrealized Depreciation	$ 0	$ 272
12 months or longer, Number of Issues | issue	2	2
12 months or longer, Fair Value	$ 14	$ 15
12 months or longer, Gross Unrealized Depreciation	3	3
Total, Fair Value	14	144
Total, Gross Unrealized Depreciation	$ 3	$ 275
Common Stocks [Member] | Technology, Media and Telecommunications [Member]
Available-for-sale
Less than 12 months, Number of Issues | issue	11	4
Less than 12 months, Fair Value	$ 536	$ 503
Less than 12 months, Gross Unrealized Depreciation	$ 20	$ 14
12 months or longer, Number of Issues | issue	1	5
12 months or longer, Fair Value	$ 10	$ 218
12 months or longer, Gross Unrealized Depreciation	10	44
Total, Fair Value	546	721
Total, Gross Unrealized Depreciation	$ 30	$ 58
Common Stocks [Member] | Financial Services [Member]
Available-for-sale
Less than 12 months, Number of Issues | issue	5	1
Less than 12 months, Fair Value	$ 252	$ 186
Less than 12 months, Gross Unrealized Depreciation	$ 61	$ 51
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	252	186
Total, Gross Unrealized Depreciation	$ 61	$ 51
Nonredeemable Preferred Stocks [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		$ 700
12 months or longer, Gross Unrealized Depreciation		7
Total, Fair Value		700
Total, Gross Unrealized Depreciation		$ 7