Investments (Fair Value and Losses by Investment Category and Length of Time in a Loss Position) (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Duration Of Unrealized Losses On Fixed Maturities Investments [Line Items]
Less than twelve months Fair Value	$ 530,615	$ 643,930
Less than 12 months Gross Unrealized Losses	9,142	20,275
Twelve months or more Fair Value	20,286	12,047
Twelve months or more Gross Unrealized Losses	1,474	1,621
Total Fair Value	550,901	655,977
Total Gross Unrealized Losses	10,616	21,896
US Treasury And Government [Member]
Duration Of Unrealized Losses On Fixed Maturities Investments [Line Items]
Less than twelve months Fair Value	3,234	3,347
Less than 12 months Gross Unrealized Losses	26	34
Twelve months or more Fair Value	0	0
Twelve months or more Gross Unrealized Losses	0	0
Total Fair Value	3,234	3,347
Total Gross Unrealized Losses	26	34
Obligations of U.S. states and their political subdivisions [Member]
Duration Of Unrealized Losses On Fixed Maturities Investments [Line Items]
Less than twelve months Fair Value	0	5,420
Less than 12 months Gross Unrealized Losses	0	588
Twelve months or more Fair Value	6,794	6,402
Twelve months or more Gross Unrealized Losses	575	982
Total Fair Value	6,794	11,822
Total Gross Unrealized Losses	575	1,570
Corporate Debt Securities [Member]
Duration Of Unrealized Losses On Fixed Maturities Investments [Line Items]
Less than twelve months Fair Value	312,686	351,306
Less than 12 months Gross Unrealized Losses	4,997	11,923
Twelve months or more Fair Value	6,004	2,704
Twelve months or more Gross Unrealized Losses	413	370
Total Fair Value	318,690	354,010
Total Gross Unrealized Losses	5,410	12,293
Asset-backed Securities [Member]
Duration Of Unrealized Losses On Fixed Maturities Investments [Line Items]
Less than twelve months Fair Value	36,910	97,575
Less than 12 months Gross Unrealized Losses	276	1,509
Twelve months or more Fair Value	986	0
Twelve months or more Gross Unrealized Losses	14	0
Total Fair Value	37,896	97,575
Total Gross Unrealized Losses	290	1,509
Commercial Mortgage Backed Securities [Member]
Duration Of Unrealized Losses On Fixed Maturities Investments [Line Items]
Less than twelve months Fair Value	100,400	86,132
Less than 12 months Gross Unrealized Losses	3,751	5,249
Twelve months or more Fair Value	6,502	2,941
Twelve months or more Gross Unrealized Losses	472	269
Total Fair Value	106,902	89,073
Total Gross Unrealized Losses	4,223	5,518
Residential Mortgage Backed Securities [Member]
Duration Of Unrealized Losses On Fixed Maturities Investments [Line Items]
Less than twelve months Fair Value	77,385	100,150
Less than 12 months Gross Unrealized Losses	92	972
Twelve months or more Fair Value	0	0
Twelve months or more Gross Unrealized Losses	0	0
Total Fair Value	77,385	100,150
Total Gross Unrealized Losses	$ 92	$ 972