Investment Securities, Amortized Cost, Fair Values, and Unrealized Gains and Losses of Securities (Details) - USD ($) $ in Thousands		Mar. 31, 2018	Dec. 31, 2017	Mar. 31, 2017
Amortized cost, fair values, and unrealized gains and losses of securities available-for-sale [Abstract]
Amortized cost		$ 502,262	$ 482,757	$ 452,976
Gross unrealized gains		435	1,016	1,958
Gross unrealized losses		6,883	2,177	2,092
Fair/Book value		495,814	481,596	452,842
Book values, estimated fair values and unrealized gains and losses of investments classified as held-to-maturity [Abstract]
Book value		53,527	54,460	57,281
Gross unrealized gains		274	776	414
Gross unrealized losses		56	0	22
Fair value		53,745	55,236	57,673
Government Agency & Government-Sponsored Entities [Member]
Amortized cost, fair values, and unrealized gains and losses of securities available-for-sale [Abstract]
Amortized cost		3,068	3,080	3,115
Gross unrealized gains		27	48	102
Gross unrealized losses		0	0	0
Fair/Book value		3,095	3,128	3,217
US Treasury Notes [Member]
Amortized cost, fair values, and unrealized gains and losses of securities available-for-sale [Abstract]
Amortized cost		144,147	144,606	104,717
Gross unrealized gains		3	0	2
Gross unrealized losses		741	442	300
Fair/Book value		143,409	144,164	104,419
US Govt SBA [Member]
Amortized cost, fair values, and unrealized gains and losses of securities available-for-sale [Abstract]
Amortized cost		27,786	29,559	34,947
Gross unrealized gains		12	29	34
Gross unrealized losses		261	208	247
Fair/Book value		27,537	29,380	34,734
Mortgage Backed Securities [Member]
Amortized cost, fair values, and unrealized gains and losses of securities available-for-sale [Abstract]
Amortized cost	[1]	324,251	302,502	309,187
Gross unrealized gains	[1]	393	939	1,820
Gross unrealized losses	[1]	5,881	1,527	1,545
Fair/Book value	[1]	318,763	301,914	309,462
Other [Member]
Amortized cost, fair values, and unrealized gains and losses of securities available-for-sale [Abstract]
Amortized cost		3,010	3,010	1,010
Gross unrealized gains		0	0	0
Gross unrealized losses		0	0	0
Fair/Book value		3,010	3,010	1,010
Obligations of States and Political Subdivisions [Member]
Book values, estimated fair values and unrealized gains and losses of investments classified as held-to-maturity [Abstract]
Book value		53,527	54,460	57,281
Gross unrealized gains		274	776	414
Gross unrealized losses		56	0	22
Fair value		$ 53,745	$ 55,236	$ 57,673

[1] All Mortgage Backed Securities consist of securities collateralized by residential real estate and were issued by an agency or government sponsored entity of the U.S. government.