Investments (Schedule of Available-for-sale Securities Reconciliation) (Details) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 503,936	$ 504,564
Gross Unrealized Gains	7,025	8,738
Gross Unrealized Losses	(1,361)	(1,419)
Estimated Fair Value	509,600	511,883
U.S. Government agencies [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	29,360	26,959
Gross Unrealized Gains	389	334
Gross Unrealized Losses	(8)	(23)
Estimated Fair Value	29,741	27,270
Mortgage-backed securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	374,966	378,339
Gross Unrealized Gains	3,425	4,299
Gross Unrealized Losses	(1,083)	(1,196)
Estimated Fair Value	377,308	381,442
State and political subdivisions [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	98,951	98,056
Gross Unrealized Gains	2,574	3,093
Gross Unrealized Losses	(270)	(200)
Estimated Fair Value	101,255	100,949
Other Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	659	1,210
Gross Unrealized Gains	$ 637	$ 1,012
Gross Unrealized Losses
Estimated Fair Value	$ 1,296	$ 2,222