Summary of Investments (Investments in Unrealized Loss Position) (Details) $ in Thousands	Sep. 30, 2015 USD ($) issue	Dec. 31, 2014 USD ($) issue
AVAILABLE-FOR-SALE
Less than 12 months, Number of Issues | issue	277	117
Less than 12 months, Fair Value	$ 479,240	$ 221,670
Less than 12 months, Gross Unrealized Depreciation	$ 9,528	$ 2,660
12 months or longer, Number of Issues | issue	90	195
12 months or longer, Fair Value	$ 142,275	$ 335,951
12 months or longer, Gross Unrealized Depreciation	7,374	11,268
Total, Fair Value	621,515	557,621
Total, Gross Unrealized Depreciation	$ 16,902	$ 13,928
Fixed Maturities [Member]
AVAILABLE-FOR-SALE
Less than 12 months, Number of Issues | issue	247	105
Less than 12 months, Fair Value	$ 475,865	$ 220,309
Less than 12 months, Gross Unrealized Depreciation	$ 9,218	$ 2,209
12 months or longer, Number of Issues | issue	78	185
12 months or longer, Fair Value	$ 141,714	$ 334,960
12 months or longer, Gross Unrealized Depreciation	6,889	11,160
Total, Fair Value	617,579	555,269
Total, Gross Unrealized Depreciation	$ 16,107	$ 13,369
U.S. Treasury [Member]
AVAILABLE-FOR-SALE
Less than 12 months, Number of Issues | issue	0	4
Less than 12 months, Fair Value	$ 0	$ 2,343
Less than 12 months, Gross Unrealized Depreciation	$ 0	$ 6
12 months or longer, Number of Issues | issue	2	4
12 months or longer, Fair Value	$ 1,652	$ 5,069
12 months or longer, Gross Unrealized Depreciation	2	46
Total, Fair Value	1,652	7,412
Total, Gross Unrealized Depreciation	$ 2	$ 52
U.S. Government Agency [Member]
AVAILABLE-FOR-SALE
Less than 12 months, Number of Issues | issue	26	11
Less than 12 months, Fair Value	$ 70,261	$ 41,064
Less than 12 months, Gross Unrealized Depreciation	$ 814	$ 70
12 months or longer, Number of Issues | issue	7	35
12 months or longer, Fair Value	$ 22,056	$ 95,198
12 months or longer, Gross Unrealized Depreciation	394	2,352
Total, Fair Value	92,317	136,262
Total, Gross Unrealized Depreciation	$ 1,208	$ 2,422
States, Municipalities and Political Subdivisions [Member] | General Obligations [Member] | Midwest [Member]
AVAILABLE-FOR-SALE
Less than 12 months, Number of Issues | issue	11	1
Less than 12 months, Fair Value	$ 11,332	$ 3,650
Less than 12 months, Gross Unrealized Depreciation	$ 94	$ 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	11,332	13,506
Total, Gross Unrealized Depreciation	$ 94	$ 170
States, Municipalities and Political Subdivisions [Member] | General Obligations [Member] | Northeast [Member]
AVAILABLE-FOR-SALE
Less than 12 months, Number of Issues | issue	7	0
Less than 12 months, Fair Value	$ 6,031	$ 0
Less than 12 months, Gross Unrealized Depreciation	$ 19	$ 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	6,031	7,377
Total, Gross Unrealized Depreciation	$ 19	$ 50
States, Municipalities and Political Subdivisions [Member] | General Obligations [Member] | South [Member]
AVAILABLE-FOR-SALE
Less than 12 months, Number of Issues | issue	11	1
Less than 12 months, Fair Value	$ 14,767	$ 3,085
Less than 12 months, Gross Unrealized Depreciation	$ 188	$ 58
12 months or longer, Number of Issues | issue	12	19
12 months or longer, Fair Value	$ 6,549	$ 13,475
12 months or longer, Gross Unrealized Depreciation	182	230
Total, Fair Value	21,316	16,560
Total, Gross Unrealized Depreciation	$ 370	$ 288
States, Municipalities and Political Subdivisions [Member] | General Obligations [Member] | West [Member]
AVAILABLE-FOR-SALE
Less than 12 months, Number of Issues | issue	13	1
Less than 12 months, Fair Value	$ 19,733	$ 1,023
Less than 12 months, Gross Unrealized Depreciation	$ 259	$ 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	19,733	3,723
Total, Gross Unrealized Depreciation	$ 259	$ 19
States, Municipalities and Political Subdivisions [Member] | Special Revenue [Member] | Midwest [Member]
AVAILABLE-FOR-SALE
Less than 12 months, Number of Issues | issue	17	9
Less than 12 months, Fair Value	$ 20,088	$ 10,219
Less than 12 months, Gross Unrealized Depreciation	$ 122	$ 41
12 months or longer, Number of Issues | issue	1	8
12 months or longer, Fair Value	$ 2,483	$ 11,631
12 months or longer, Gross Unrealized Depreciation	44	105
Total, Fair Value	22,571	21,850
Total, Gross Unrealized Depreciation	$ 166	$ 146
States, Municipalities and Political Subdivisions [Member] | Special Revenue [Member] | Northeast [Member]
AVAILABLE-FOR-SALE
Less than 12 months, Number of Issues | issue	1
Less than 12 months, Fair Value	$ 4,814
Less than 12 months, Gross Unrealized Depreciation	$ 153
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	4,814
Total, Gross Unrealized Depreciation	$ 153
States, Municipalities and Political Subdivisions [Member] | Special Revenue [Member] | South [Member]
AVAILABLE-FOR-SALE
Less than 12 months, Number of Issues | issue	8	6
Less than 12 months, Fair Value	$ 12,527	$ 12,882
Less than 12 months, Gross Unrealized Depreciation	$ 84	$ 11
12 months or longer, Number of Issues | issue	2	3
12 months or longer, Fair Value	$ 1,828	$ 2,137
12 months or longer, Gross Unrealized Depreciation	28	52
Total, Fair Value	14,355	15,019
Total, Gross Unrealized Depreciation	$ 112	$ 63
States, Municipalities and Political Subdivisions [Member] | Special Revenue [Member] | West [Member]
AVAILABLE-FOR-SALE
Less than 12 months, Number of Issues | issue	8	0
Less than 12 months, Fair Value	$ 8,447	$ 0
Less than 12 months, Gross Unrealized Depreciation	$ 24	$ 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	8,447	3,671
Total, Gross Unrealized Depreciation	$ 24	$ 6
Foreign Bonds [Member]
AVAILABLE-FOR-SALE
Less than 12 months, Number of Issues | issue	9	6
Less than 12 months, Fair Value	$ 15,153	$ 17,158
Less than 12 months, Gross Unrealized Depreciation	$ 1,628	$ 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	15,153	17,158
Total, Gross Unrealized Depreciation	$ 1,628	$ 446
Public Utilities [Member]
AVAILABLE-FOR-SALE
Less than 12 months, Number of Issues | issue	13	10
Less than 12 months, Fair Value	$ 28,383	$ 21,839
Less than 12 months, Gross Unrealized Depreciation	$ 376	$ 194
12 months or longer, Number of Issues | issue	5	4
12 months or longer, Fair Value	$ 2,926	$ 3,611
12 months or longer, Gross Unrealized Depreciation	312	294
Total, Fair Value	31,309	25,450
Total, Gross Unrealized Depreciation	$ 688	$ 488
Corporate Bonds [Member] | Energy [Member]
AVAILABLE-FOR-SALE
Less than 12 months, Number of Issues | issue	7	8
Less than 12 months, Fair Value	$ 14,922	$ 17,416
Less than 12 months, Gross Unrealized Depreciation	$ 884	$ 420
12 months or longer, Number of Issues | issue	3	3
12 months or longer, Fair Value	$ 6,876	$ 7,061
12 months or longer, Gross Unrealized Depreciation	507	373
Total, Fair Value	21,798	24,477
Total, Gross Unrealized Depreciation	$ 1,391	$ 793
Corporate Bonds [Member] | Industrials [Member]
AVAILABLE-FOR-SALE
Less than 12 months, Number of Issues | issue	20	8
Less than 12 months, Fair Value	$ 35,955	$ 17,103
Less than 12 months, Gross Unrealized Depreciation	$ 1,282	$ 362
12 months or longer, Number of Issues | issue	3	3
12 months or longer, Fair Value	$ 7,878	$ 9,592
12 months or longer, Gross Unrealized Depreciation	3,115	1,792
Total, Fair Value	43,833	26,695
Total, Gross Unrealized Depreciation	$ 4,397	$ 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	$ 46,527	$ 28,344
Less than 12 months, Gross Unrealized Depreciation	$ 647	$ 258
12 months or longer, Number of Issues | issue	4	7
12 months or longer, Fair Value	$ 2,502	$ 10,064
12 months or longer, Gross Unrealized Depreciation	4	66
Total, Fair Value	49,029	38,408
Total, Gross Unrealized Depreciation	$ 651	$ 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	$ 31,567	$ 8,244
Less than 12 months, Gross Unrealized Depreciation	$ 505	$ 36
12 months or longer, Number of Issues | issue	2	3
12 months or longer, Fair Value	$ 3,806	$ 7,104
12 months or longer, Gross Unrealized Depreciation	85	174
Total, Fair Value	35,373	15,348
Total, Gross Unrealized Depreciation	$ 590	$ 210
Corporate Bonds [Member] | Technology, Media and Telecommunications [Member]
AVAILABLE-FOR-SALE
Less than 12 months, Number of Issues | issue	19	4
Less than 12 months, Fair Value	$ 53,402	$ 8,860
Less than 12 months, Gross Unrealized Depreciation	$ 850	$ 68
12 months or longer, Number of Issues | issue	2	4
12 months or longer, Fair Value	$ 8,987	$ 15,742
12 months or longer, Gross Unrealized Depreciation	498	731
Total, Fair Value	62,389	24,602
Total, Gross Unrealized Depreciation	$ 1,348	$ 799
Corporate Bonds [Member] | Financial Services [Member]
AVAILABLE-FOR-SALE
Less than 12 months, Number of Issues | issue	21	3
Less than 12 months, Fair Value	$ 42,848	$ 5,908
Less than 12 months, Gross Unrealized Depreciation	$ 633	$ 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	42,848	12,039
Total, Gross Unrealized Depreciation	$ 633	$ 87
Mortgage-Backed Securities [Member]
AVAILABLE-FOR-SALE
Less than 12 months, Number of Issues | issue	2	9
Less than 12 months, Fair Value	$ 1,503	$ 425
Less than 12 months, Gross Unrealized Depreciation	$ 15	$ 21
12 months or longer, Number of Issues | issue	4	2
12 months or longer, Fair Value	$ 198	$ 1,991
12 months or longer, Gross Unrealized Depreciation	10	25
Total, Fair Value	1,701	2,416
Total, Gross Unrealized Depreciation	$ 25	$ 46
Collateralized Mortgage Obligations [Member]
AVAILABLE-FOR-SALE
Less than 12 months, Number of Issues | issue	23	10
Less than 12 months, Fair Value	$ 35,007	$ 20,746
Less than 12 months, Gross Unrealized Depreciation	$ 472	$ 112
12 months or longer, Number of Issues | issue	31	56
12 months or longer, Fair Value	$ 73,973	$ 122,550
12 months or longer, Gross Unrealized Depreciation	1,708	4,694
Total, Fair Value	108,980	143,296
Total, Gross Unrealized Depreciation	$ 2,180	$ 4,806
Asset-backed Securities [Member]
AVAILABLE-FOR-SALE
Less than 12 months, Number of Issues | issue	1
Less than 12 months, Fair Value	$ 2,598
Less than 12 months, Gross Unrealized Depreciation	$ 169
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	2,598
Total, Gross Unrealized Depreciation	$ 169
Equity Securities [Member]
AVAILABLE-FOR-SALE
Less than 12 months, Number of Issues | issue	30	12
Less than 12 months, Fair Value	$ 3,375	$ 1,361
Less than 12 months, Gross Unrealized Depreciation	$ 310	$ 451
12 months or longer, Number of Issues | issue	12	10
12 months or longer, Fair Value	$ 561	$ 991
12 months or longer, Gross Unrealized Depreciation	485	108
Total, Fair Value	3,936	2,352
Total, Gross Unrealized Depreciation	$ 795	$ 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	$ 145	$ 0
12 months or longer, Gross Unrealized Depreciation	163	0
Total, Fair Value	145	263
Total, Gross Unrealized Depreciation	$ 163	$ 44
Common Stocks [Member] | Energy [Member]
AVAILABLE-FOR-SALE
Less than 12 months, Number of Issues | issue	8
Less than 12 months, Fair Value	$ 1,934
Less than 12 months, Gross Unrealized Depreciation	$ 159
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	1,934
Total, Gross Unrealized Depreciation	$ 159
Common Stocks [Member] | Industrials [Member]
AVAILABLE-FOR-SALE
Less than 12 months, Number of Issues | issue	5	3
Less than 12 months, Fair Value	$ 301	$ 280
Less than 12 months, Gross Unrealized Depreciation	$ 11	$ 70
12 months or longer, Number of Issues | issue	4	2
12 months or longer, Fair Value	$ 219	$ 58
12 months or longer, Gross Unrealized Depreciation	239	54
Total, Fair Value	520	338
Total, Gross Unrealized Depreciation	$ 250	$ 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	$ 13	$ 15
12 months or longer, Gross Unrealized Depreciation	5	3
Total, Fair Value	13	144
Total, Gross Unrealized Depreciation	$ 5	$ 275
Common Stocks [Member] | Technology, Media and Telecommunications [Member]
AVAILABLE-FOR-SALE
Less than 12 months, Number of Issues | issue	10	4
Less than 12 months, Fair Value	$ 478	$ 503
Less than 12 months, Gross Unrealized Depreciation	$ 71	$ 14
12 months or longer, Number of Issues | issue	2	5
12 months or longer, Fair Value	$ 12	$ 218
12 months or longer, Gross Unrealized Depreciation	14	44
Total, Fair Value	490	721
Total, Gross Unrealized Depreciation	$ 85	$ 58
Common Stocks [Member] | Financial Services [Member]
AVAILABLE-FOR-SALE
Less than 12 months, Number of Issues | issue	6	1
Less than 12 months, Fair Value	$ 311	$ 186
Less than 12 months, Gross Unrealized Depreciation	$ 67	$ 51
12 months or longer, Number of Issues | issue	1	0
12 months or longer, Fair Value	$ 172	$ 0
12 months or longer, Gross Unrealized Depreciation	64	0
Total, Fair Value	483	186
Total, Gross Unrealized Depreciation	$ 131	$ 51
Nonredeemable Preferred Stocks [Member]
AVAILABLE-FOR-SALE
Less than 12 months, Number of Issues | issue	1	0
Less than 12 months, Fair Value	$ 351	$ 0
Less than 12 months, Gross Unrealized Depreciation	$ 2	$ 0
12 months or longer, Number of Issues | issue	0	1
12 months or longer, Fair Value	$ 0	$ 700
12 months or longer, Gross Unrealized Depreciation	0	7
Total, Fair Value	351	700
Total, Gross Unrealized Depreciation	$ 2	$ 7