Investments - Schedule of Unrealized Loss on Investments (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Schedule of Available-for-sale Securities [Line Items]
Less than 12 months, Fair Vaule	$ 239,510	$ 46,905
Less than 12 months, Unrealized Losses	7,227	265
12 months or more, Fair Value	11,821	14,655
12 months or more, Unrealized Losses	821	477
Total, Fair Value	251,331	61,560
Total, Unrealized Losses	8,048	742
Obligations of U.S. government sponsored enterprises
Schedule of Available-for-sale Securities [Line Items]
Less than 12 months, Fair Vaule	30,355
Less than 12 months, Unrealized Losses	305
12 months or more, Fair Value	0
12 months or more, Unrealized Losses	0
Total, Fair Value	30,355
Total, Unrealized Losses	305
Obligations of the state and political subdivisions
Schedule of Available-for-sale Securities [Line Items]
Less than 12 months, Fair Vaule	20,306	6,434
Less than 12 months, Unrealized Losses	1,230	122
12 months or more, Fair Value	3,042	3,389
12 months or more, Unrealized Losses	358	356
Total, Fair Value	23,348	9,823
Total, Unrealized Losses	1,588	478
Residential mortgage-backed securities
Schedule of Available-for-sale Securities [Line Items]
Less than 12 months, Fair Vaule	188,849	40,471
Less than 12 months, Unrealized Losses	5,692	143
12 months or more, Fair Value	8,779	11,266
12 months or more, Unrealized Losses	463	121
Total, Fair Value	197,628	51,737
Total, Unrealized Losses	$ 6,155	$ 264