Investments - Schedule of Available-for-sale Securities Reconciliation (Details) (USD $)	9 Months Ended
	Sep. 30, 2013	Dec. 31, 2012
Available for sale securities:
Amortized Cost	$ 456,289,000	$ 627,462,000
Gross Unrealized Gains	4,805,000	13,492,000
Gross Unrealized Losses	(8,048,000)	(742,000)
Fair Value	453,046,000	640,212,000
Percentage of shareholders' equity held by one issuer, maximum	10.00%	10.00%
Available-for-sale securities pledged as collateral, fair value	227,500,000	359,300,000
Mortgage-backed securities, weighted average life	5 years
Obligations of U.S. Government sponsored enterprises
Available for sale securities:
Amortized Cost	93,680,000	149,039,000
Gross Unrealized Gains	599,000	3,329,000
Gross Unrealized Losses	(305,000)	0
Fair Value	93,974,000	152,368,000
Obligations of states and political subdivisions
Available for sale securities:
Amortized Cost	51,702,000	51,202,000
Gross Unrealized Gains	1,079,000	2,279,000
Gross Unrealized Losses	(1,588,000)	(478,000)
Fair Value	51,193,000	53,003,000
Residential mortgage-backed securities
Available for sale securities:
Amortized Cost	310,907,000	427,221,000
Gross Unrealized Gains	3,127,000	7,884,000
Gross Unrealized Losses	(6,155,000)	(264,000)
Fair Value	$ 307,879,000	$ 434,841,000