Summary of Significant Accounting Policies - Dividend (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Jan. 17, 2017	Dec. 31, 2015	Dec. 31, 2014
90-Days or Greater Past Due Loans
Period from due date after which accrual of interest income is discontinued	90 days
Accumulated other comprehensive income (loss) breakdown
Unrealized gains on securities	$ 2,200,000
Unrealized losses on securities		$ 8,200,000
Unrealized Loss on Price Risk Cash Flow Derivatives, before Tax	760,000	596,000
Allowance for Loan Losses
Loans and Leases Receivable, Allowance	17,461,000	16,158,000		$ 16,223,000	$ 21,637,000
Dividends Payable, Amount Per Share			$ 0.01
All other
Allowance for Loan Losses
Loans and Leases Receivable, Allowance	$ 542,000	$ 435,000		$ 1,965,000	$ 2,506,000