Disclosures about Fair Value of Financial Instruments (Summary of the Company's Financial Instruments) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Fair Value Disclosures [Abstract]
Cash and cash equivalents, Carrying Amount	$ 228,110	$ 266,743	$ 253,172	$ 294,335
Investment in securities, Carrying Amount	470,523	390,552
Loans, net, Carrying Amount	676,026	654,691
Accrued interest receivable, Carrying Amount	7,413	6,543
Assets, Carrying Amount	1,382,072	1,318,529
Cash and cash equivalents, Fair Value	228,110	266,743
Investment in securities, Fair Value	470,523	390,552
Loans, net, Fair Value	675,020	652,028
Accrued interest receivable, Fair Value	7,413	6,543
Assets, Fair Value	1,381,066	1,315,866
Deposits, Carrying Amount	678,088	621,961
Accounts and drafts payable, Carrying Amount	661,888	642,287
Accrued interest payable, Carrying Amount	55	46
Liabilities, Carrying Amount	1,340,031	1,264,294
Deposits, Fair Value	678,346	622,173
Accounts and drafts payable, Fair Value	661,888	642,287
Accrued interest payable, Fair Value	55	46
Liabilities, Fair Value	$ 1,340,289	$ 1,264,506