Investments (Fair Value and Losses by Investment Category and Length of Time in a Loss Position) (Details) - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
Duration Of Unrealized Losses On Fixed Maturities Investments [Line Items]
Less than twelve months Fair Value	$ 411,336	$ 322,351
Less than 12 months Gross Unrealized Losses	12,769	5,969
Twelve months or more Fair Value	44,429	58,991
Twelve months or more Gross Unrealized Losses	2,156	1,152
Total Fair Value	455,765	381,342
Total Gross Unrealized Losses	14,925	7,121
U.S. Treasury securities and obligations of U.S. government authorities and agencies
Duration Of Unrealized Losses On Fixed Maturities Investments [Line Items]
Less than twelve months Fair Value	0	2,676
Less than 12 months Gross Unrealized Losses	0	10
Twelve months or more Fair Value	0	0
Twelve months or more Gross Unrealized Losses	0	0
Total Fair Value	0	2,676
Total Gross Unrealized Losses	0	10
Obligations of U.S. states and their political subdivisions
Duration Of Unrealized Losses On Fixed Maturities Investments [Line Items]
Less than twelve months Fair Value	6,716	0
Less than 12 months Gross Unrealized Losses	579	0
Twelve months or more Fair Value	0	7,305
Twelve months or more Gross Unrealized Losses	0	20
Total Fair Value	6,716	7,305
Total Gross Unrealized Losses	579	20
Foreign government bonds
Duration Of Unrealized Losses On Fixed Maturities Investments [Line Items]
Less than twelve months Fair Value	3,742	4,632
Less than 12 months Gross Unrealized Losses	5	4
Twelve months or more Fair Value	0	0
Twelve months or more Gross Unrealized Losses	0	0
Total Fair Value	3,742	4,632
Total Gross Unrealized Losses	5	4
Public utilities
Duration Of Unrealized Losses On Fixed Maturities Investments [Line Items]
Less than twelve months Fair Value	32,824	18,222
Less than 12 months Gross Unrealized Losses	1,827	1,321
Twelve months or more Fair Value	6,202	2,174
Twelve months or more Gross Unrealized Losses	915	272
Total Fair Value	39,026	20,396
Total Gross Unrealized Losses	2,742	1,593
All other corporate securities
Duration Of Unrealized Losses On Fixed Maturities Investments [Line Items]
Less than twelve months Fair Value	339,705	260,414
Less than 12 months Gross Unrealized Losses	10,134	4,462
Twelve months or more Fair Value	14,661	9,403
Twelve months or more Gross Unrealized Losses	1,080	429
Total Fair Value	354,366	269,817
Total Gross Unrealized Losses	11,214	4,891
Asset-backed securities
Duration Of Unrealized Losses On Fixed Maturities Investments [Line Items]
Less than twelve months Fair Value	8,054	31,756
Less than 12 months Gross Unrealized Losses	33	58
Twelve months or more Fair Value	23,552	32,732
Twelve months or more Gross Unrealized Losses	161	333
Total Fair Value	31,606	64,488
Total Gross Unrealized Losses	194	391
Commercial mortgage-backed securities
Duration Of Unrealized Losses On Fixed Maturities Investments [Line Items]
Less than twelve months Fair Value	20,295	4,309
Less than 12 months Gross Unrealized Losses	191	108
Twelve months or more Fair Value	14	7,377
Twelve months or more Gross Unrealized Losses	0	98
Total Fair Value	20,309	11,686
Total Gross Unrealized Losses	191	206
Residential mortgage-backed securities
Duration Of Unrealized Losses On Fixed Maturities Investments [Line Items]
Less than twelve months Fair Value	0	342
Less than 12 months Gross Unrealized Losses	0	6
Twelve months or more Fair Value	0	0
Twelve months or more Gross Unrealized Losses	0	0
Total Fair Value	0	342
Total Gross Unrealized Losses	0	6
Equity securities, available-for-sale
Duration Of Unrealized Losses On Fixed Maturities Investments [Line Items]
Less than twelve months Fair Value	0	0
Less than 12 months Gross Unrealized Losses	0	0
Twelve months or more Fair Value	0	0
Twelve months or more Gross Unrealized Losses	0	0
Total Fair Value	0	0
Total Gross Unrealized Losses	$ 0	$ 0