Investments (Summary of Amortized Cost and Fair Values of General Obligation and Revenue Bonds) (Details) - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
Amortized Cost And Estimated Fair Value Of Investment Securities Available For Sale By By Type Of Bonds [Line Items]
Amortized Cost	$ 502,431	$ 504,564
Fair Value	506,919	511,883
States and Political Subdivisions [Member]
Amortized Cost And Estimated Fair Value Of Investment Securities Available For Sale By By Type Of Bonds [Line Items]
Amortized Cost	97,154	98,056
Fair Value	99,055	100,949
General obligation bonds [Member] | States and Political Subdivisions [Member]
Amortized Cost And Estimated Fair Value Of Investment Securities Available For Sale By By Type Of Bonds [Line Items]
Amortized Cost	80,213	78,470
Fair Value	81,849	80,854
General obligation bonds [Member] | States and Political Subdivisions [Member] | California [Member]
Amortized Cost And Estimated Fair Value Of Investment Securities Available For Sale By By Type Of Bonds [Line Items]
Amortized Cost	20,624	20,078
Fair Value	21,702	21,288
General obligation bonds [Member] | States and Political Subdivisions [Member] | Texas [Member]
Amortized Cost And Estimated Fair Value Of Investment Securities Available For Sale By By Type Of Bonds [Line Items]
Amortized Cost	14,261	14,489
Fair Value	14,297	14,675
General obligation bonds [Member] | States and Political Subdivisions [Member] | Illinois [Member]
Amortized Cost And Estimated Fair Value Of Investment Securities Available For Sale By By Type Of Bonds [Line Items]
Amortized Cost	8,593	8,272
Fair Value	8,645	8,394
General obligation bonds [Member] | States and Political Subdivisions [Member] | Ohio [Member]
Amortized Cost And Estimated Fair Value Of Investment Securities Available For Sale By By Type Of Bonds [Line Items]
Amortized Cost	7,857	7,456
Fair Value	7,865	7,555
General obligation bonds [Member] | States and Political Subdivisions [Member] | Washington [Member]
Amortized Cost And Estimated Fair Value Of Investment Securities Available For Sale By By Type Of Bonds [Line Items]
Amortized Cost	5,936	5,966
Fair Value	6,055	6,126
General obligation bonds [Member] | States and Political Subdivisions [Member] | Utah [Member]
Amortized Cost And Estimated Fair Value Of Investment Securities Available For Sale By By Type Of Bonds [Line Items]
Amortized Cost	955	956
Fair Value	968	984
General obligation bonds [Member] | States and Political Subdivisions [Member] | Other [Member]
Amortized Cost And Estimated Fair Value Of Investment Securities Available For Sale By By Type Of Bonds [Line Items]
Amortized Cost	21,987	21,253
Fair Value	22,317	21,832
Revenue bonds [Member]
Amortized Cost And Estimated Fair Value Of Investment Securities Available For Sale By By Type Of Bonds [Line Items]
Amortized Cost	16,941	19,586
Fair Value	17,206	20,095
Revenue bonds [Member] | Water [Member]
Amortized Cost And Estimated Fair Value Of Investment Securities Available For Sale By By Type Of Bonds [Line Items]
Amortized Cost	3,722	7,100
Fair Value	3,780	7,278
Revenue bonds [Member] | College & University [Member]
Amortized Cost And Estimated Fair Value Of Investment Securities Available For Sale By By Type Of Bonds [Line Items]
Amortized Cost	3,210	2,723
Fair Value	3,296	2,834
Revenue bonds [Member] | Sales Tax [Member]
Amortized Cost And Estimated Fair Value Of Investment Securities Available For Sale By By Type Of Bonds [Line Items]
Amortized Cost	2,295	2,361
Fair Value	2,322	2,405
Revenue bonds [Member] | Electric & Power [Member]
Amortized Cost And Estimated Fair Value Of Investment Securities Available For Sale By By Type Of Bonds [Line Items]
Amortized Cost	1,876	1,880
Fair Value	1,891	1,914
Revenue bonds [Member] | Lease [Member]
Amortized Cost And Estimated Fair Value Of Investment Securities Available For Sale By By Type Of Bonds [Line Items]
Amortized Cost	2,202	1,356
Fair Value	2,178	1,362
Revenue bonds [Member] | Other [Member]
Amortized Cost And Estimated Fair Value Of Investment Securities Available For Sale By By Type Of Bonds [Line Items]
Amortized Cost	3,636	4,166
Fair Value	3,739	4,302
Revenue bonds [Member] | States and Political Subdivisions [Member]
Amortized Cost And Estimated Fair Value Of Investment Securities Available For Sale By By Type Of Bonds [Line Items]
Amortized Cost	16,941	19,586
Fair Value	17,206	20,095
Revenue bonds [Member] | States and Political Subdivisions [Member] | California [Member]
Amortized Cost And Estimated Fair Value Of Investment Securities Available For Sale By By Type Of Bonds [Line Items]
Amortized Cost	1,605	2,174
Fair Value	1,642	2,233
Revenue bonds [Member] | States and Political Subdivisions [Member] | Texas [Member]
Amortized Cost And Estimated Fair Value Of Investment Securities Available For Sale By By Type Of Bonds [Line Items]
Amortized Cost	3,756	3,273
Fair Value	3,842	3,387
Revenue bonds [Member] | States and Political Subdivisions [Member] | Illinois [Member]
Amortized Cost And Estimated Fair Value Of Investment Securities Available For Sale By By Type Of Bonds [Line Items]
Amortized Cost	292	294
Fair Value	291	294
Revenue bonds [Member] | States and Political Subdivisions [Member] | Ohio [Member]
Amortized Cost And Estimated Fair Value Of Investment Securities Available For Sale By By Type Of Bonds [Line Items]
Amortized Cost	319	321
Fair Value	324	332
Revenue bonds [Member] | States and Political Subdivisions [Member] | Washington [Member]
Amortized Cost And Estimated Fair Value Of Investment Securities Available For Sale By By Type Of Bonds [Line Items]
Amortized Cost	1,166	1,167
Fair Value	1,187	1,197
Revenue bonds [Member] | States and Political Subdivisions [Member] | Utah [Member]
Amortized Cost And Estimated Fair Value Of Investment Securities Available For Sale By By Type Of Bonds [Line Items]
Amortized Cost	4,441	3,769
Fair Value	4,440	3,834
Revenue bonds [Member] | States and Political Subdivisions [Member] | Other [Member]
Amortized Cost And Estimated Fair Value Of Investment Securities Available For Sale By By Type Of Bonds [Line Items]
Amortized Cost	5,362	8,588
Fair Value	$ 5,480	$ 8,818