Investments (Schedule of Available-for-sale Securities Reconciliation) (Details) - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 502,431	$ 504,564
Gross Unrealized Gains	7,051	8,738
Gross Unrealized Losses	(2,563)	(1,419)
Estimated Fair Value	506,919	511,883
U.S. Government agencies [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	25,815	26,959
Gross Unrealized Gains	350	334
Gross Unrealized Losses	(21)	(23)
Estimated Fair Value	26,144	27,270
Mortgage-backed securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	378,713	378,339
Gross Unrealized Gains	3,541	4,299
Gross Unrealized Losses	(2,023)	(1,196)
Estimated Fair Value	380,231	381,442
State and political subdivisions [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	97,154	98,056
Gross Unrealized Gains	2,420	3,093
Gross Unrealized Losses	(519)	(200)
Estimated Fair Value	99,055	100,949
Other Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	749	1,210
Gross Unrealized Gains	$ 740	$ 1,012
Gross Unrealized Losses
Estimated Fair Value	$ 1,489	$ 2,222