Investments (Summary of Amortized Cost and Fair Values of General Obligation and Revenue Bonds) (Details) - USD ($) $ in Thousands	Sep. 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	$ 503,936	$ 504,564
Fair Value	509,600	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	98,951	98,056
Fair Value	101,255	100,949
General obligation bonds [Member]
Amortized Cost And Estimated Fair Value Of Investment Securities Available For Sale By By Type Of Bonds [Line Items]
Amortized Cost	82,501	78,470
Fair Value	84,503	80,854
General obligation bonds [Member] | California [Member]
Amortized Cost And Estimated Fair Value Of Investment Securities Available For Sale By By Type Of Bonds [Line Items]
Amortized Cost	20,023	20,078
Fair Value	21,110	21,288
General obligation bonds [Member] | Texas [Member]
Amortized Cost And Estimated Fair Value Of Investment Securities Available For Sale By By Type Of Bonds [Line Items]
Amortized Cost	14,718	14,489
Fair Value	14,908	14,675
General obligation bonds [Member] | Illinois [Member]
Amortized Cost And Estimated Fair Value Of Investment Securities Available For Sale By By Type Of Bonds [Line Items]
Amortized Cost	10,014	8,272
Fair Value	10,089	8,394
General obligation bonds [Member] | Ohio [Member]
Amortized Cost And Estimated Fair Value Of Investment Securities Available For Sale By By Type Of Bonds [Line Items]
Amortized Cost	8,254	7,456
Fair Value	8,317	7,555
General obligation bonds [Member] | Washington [Member]
Amortized Cost And Estimated Fair Value Of Investment Securities Available For Sale By By Type Of Bonds [Line Items]
Amortized Cost	5,920	5,966
Fair Value	6,067	6,126
General obligation bonds [Member] | Utah [Member]
Amortized Cost And Estimated Fair Value Of Investment Securities Available For Sale By By Type Of Bonds [Line Items]
Amortized Cost	954	956
Fair Value	976	984
General obligation 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	22,618	21,253
Fair Value	23,036	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	16,450	19,586
Fair Value	16,752	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	3,653	7,100
Fair Value	3,712	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	3,201	2,723
Fair Value	3,300	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	2,292	2,361
Fair Value	2,328	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	1,874	1,880
Fair Value	1,884	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	2,198	1,356
Fair Value	2,199	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	3,232	4,166
Fair Value	3,329	4,302
Revenue bonds [Member] | California [Member]
Amortized Cost And Estimated Fair Value Of Investment Securities Available For Sale By By Type Of Bonds [Line Items]
Amortized Cost	1,003	2,174
Fair Value	1,031	2,233
Revenue bonds [Member] | Texas [Member]
Amortized Cost And Estimated Fair Value Of Investment Securities Available For Sale By By Type Of Bonds [Line Items]
Amortized Cost	3,744	3,273
Fair Value	3,845	3,387
Revenue bonds [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	293	294
Revenue bonds [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	321	332
Revenue bonds [Member] | Washington [Member]
Amortized Cost And Estimated Fair Value Of Investment Securities Available For Sale By By Type Of Bonds [Line Items]
Amortized Cost	1,370	1,167
Fair Value	1,389	1,197
Revenue bonds [Member] | Utah [Member]
Amortized Cost And Estimated Fair Value Of Investment Securities Available For Sale By By Type Of Bonds [Line Items]
Amortized Cost	4,437	3,769
Fair Value	4,469	3,834
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	5,285	8,588
Fair Value	$ 5,404	$ 8,818