Fair Value of Assets and Liabilities, Part II (Details) - USD ($)		3 Months Ended	12 Months Ended
		Mar. 31, 2018	Dec. 31, 2017
Foreclosed Assets Held for Sale [Abstract]
Other real estate owned		$ 1,951,000	$ 2,754,000
Assets Measured On Recurring And Nonrecurring Basis Valuation Techniques [Abstract]
Assets, Fair Value Disclosure, Recurring		2,522,000	2,548,000
Financial Assets [Abstract]
Available-for-sale securities		569,862,000	578,579,000
Held-to-maturity Securities		69,358,000	69,332,000
Held-to-maturity Securities, Fair Value		67,631,000	68,457,000
Financial Liabilities [Abstract]
Other borrowings		9,375,000	10,313,000
Carrying Amount [Member]
Financial Assets [Abstract]
Cash and due from banks		54,344,000	88,388,000
Federal funds sold		491,000	491,000
Certificates of deposit investments		1,685,000	1,685,000
Available-for-sale securities		569,862,000	578,579,000
Held-to-maturity Securities		69,358,000	69,332,000
Loans held for sale		1,309,000	1,025,000
Loans net of allowance for loan losses		1,955,617,000	1,918,499,000
Interest receivable		10,182,000	10,832,000
Federal Reserve Bank stock		5,160,000	5,160,000
Federal Home Loan Bank stock		2,407,000	2,407,000
Financial Liabilities [Abstract]
Deposits		2,291,891,000	2,274,639,000
Securities sold under agreements to repurchase		132,435,000	155,388,000
Interest payable		709,000	602,000
Federal Home Loan Bank borrowings		60,024,000	60,038,000
Other Liabilities, Fair Value Disclosure			10,313,000
Other borrowings		9,375,000
Junior subordinated debentures		24,021,000	24,000,000
Fair Value [Member]
Financial Assets [Abstract]
Cash and due from banks		54,344,000	88,388,000
Federal funds sold		491,000	491,000
Certificates of deposit investments		1,682,000	1,692,000
Available-for-sale securities		569,862,000	578,579,000
Held-to-maturity Securities, Fair Value		67,631,000	68,457,000
Loans held for sale		1,309,000	1,025,000
Loans net of allowance for loan losses		1,887,726,000	1,899,678,000
Interest receivable		10,182,000	10,832,000
Federal Reserve Bank stock		5,160,000	5,160,000
Federal Home Loan Bank stock		2,407,000	2,407,000
Financial Liabilities [Abstract]
Deposits		2,287,907,000	2,272,868,000
Securities sold under agreements to repurchase		132,420,000	155,394,000
Interest payable		709,000	602,000
Federal Home Loan Bank borrowings		59,599,000	59,968,000
Other Liabilities, Fair Value Disclosure			10,313,000
Other borrowings		9,375,000
Junior subordinated debentures		18,899,000	18,050,000
Fair Value, Measurements, Nonrecurring [Member] | Carrying Amount [Member]
Foreclosed Assets Held for Sale [Abstract]
Other real estate owned		1,951,000
Fair Value, Measurements, Nonrecurring [Member] | Fair Value [Member]
Foreclosed Assets Held for Sale [Abstract]
Other real estate owned		24,000
Quoted Prices in Active Markets for Identical Assets (Level 1)
Financial Assets [Abstract]
Cash and due from banks		54,344,000	88,388,000
Federal funds sold		491,000	491,000
Certificates of deposit investments		0	0
Available-for-sale securities		192,000	172,000
Held-to-maturity Securities, Fair Value		0	0
Loans held for sale		0	0
Loans net of allowance for loan losses		0	0
Interest receivable		0	0
Federal Reserve Bank stock		0	0
Federal Home Loan Bank stock		0	0
Financial Liabilities [Abstract]
Deposits		0	0
Securities sold under agreements to repurchase		0	0
Interest payable		0	0
Federal Home Loan Bank borrowings		0	0
Other borrowings		0	0
Junior subordinated debentures		0	0
Significant Other Observable Inputs (Level 2)
Financial Assets [Abstract]
Cash and due from banks		0	0
Federal funds sold		0	0
Certificates of deposit investments		1,682,000	1,692,000
Available-for-sale securities		567,148,000	575,859,000
Held-to-maturity Securities, Fair Value		67,631,000	68,457,000
Loans held for sale		1,309,000	1,025,000
Loans net of allowance for loan losses		0	0
Interest receivable		10,182,000	10,832,000
Federal Reserve Bank stock		5,160,000	5,160,000
Federal Home Loan Bank stock		2,407,000	2,407,000
Financial Liabilities [Abstract]
Deposits		1,949,676,000	1,930,604,000
Securities sold under agreements to repurchase		132,420,000	155,394,000
Interest payable		709,000	602,000
Federal Home Loan Bank borrowings		59,599,000	59,968,000
Other borrowings		9,375,000	10,313,000
Junior subordinated debentures		18,899,000	18,050,000
Significant Unobservable Inputs (Level 3)
Financial Assets [Abstract]
Cash and due from banks		0	0
Federal funds sold		0	0
Certificates of deposit investments		0	0
Available-for-sale securities		2,522,000	2,548,000
Held-to-maturity Securities, Fair Value		0	0
Loans held for sale		0	0
Loans net of allowance for loan losses		1,887,726,000	1,899,678,000
Interest receivable		0	0
Federal Reserve Bank stock		0	0
Federal Home Loan Bank stock		0	0
Financial Liabilities [Abstract]
Deposits		338,231,000	342,264,000
Securities sold under agreements to repurchase		0	0
Interest payable		0	0
Federal Home Loan Bank borrowings		0	0
Other borrowings		0	0
Junior subordinated debentures		$ 0	$ 0
Trust preferred securities | Significant Unobservable Inputs (Level 3) | Discounted Cash Flow [Member]
Assets Measured On Recurring And Nonrecurring Basis Valuation Techniques [Abstract]
Discount rate (in hundredths)		11.70%	12.70%
Constant prepayment rate (in hundredths)	[1]	1.50%	1.30%
Cumulative projected prepayments (in hundredths)		23.90%	21.60%
Probability of default (in hundredths)		0.50%	0.50%
Loss severity (in hundredths)		97.80%	97.70%
Projected cures given deferral (in hundredths)		0.00%	0.00%
Impaired loans (collateral dependent) | Fair Value, Measurements, Nonrecurring [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Assets, Fair Value Disclosure, Nonrecurring		$ 3,489,000	$ 3,053,000
Impaired loans (collateral dependent) | Quoted Prices in Active Markets for Identical Assets (Level 1) | Fair Value, Measurements, Nonrecurring [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Assets, Fair Value Disclosure, Nonrecurring		0	0
Impaired loans (collateral dependent) | Significant Other Observable Inputs (Level 2) | Fair Value, Measurements, Nonrecurring [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Assets, Fair Value Disclosure, Nonrecurring		$ 0	$ 0
Impaired loans (collateral dependent) | Significant Unobservable Inputs (Level 3) | Minimum [Member] | Third Party Valuations [Member]
Assets Measured On Recurring And Nonrecurring Basis Valuation Techniques [Abstract]
Discount to reflect realizable value		0.00%	0.00%
Impaired loans (collateral dependent) | Significant Unobservable Inputs (Level 3) | Maximum [Member] | Third Party Valuations [Member]
Assets Measured On Recurring And Nonrecurring Basis Valuation Techniques [Abstract]
Discount to reflect realizable value		40.00%	40.00%
Impaired loans (collateral dependent) | Significant Unobservable Inputs (Level 3) | Weighted Average [Member] | Third Party Valuations [Member]
Assets Measured On Recurring And Nonrecurring Basis Valuation Techniques [Abstract]
Discount to reflect realizable value		20.00%	20.00%
Impaired loans (collateral dependent) | Significant Unobservable Inputs (Level 3) | Fair Value, Measurements, Nonrecurring [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Assets, Fair Value Disclosure, Nonrecurring		$ 3,489,000	$ 3,053,000
Assets Held-for-sale [Member] | Fair Value, Measurements, Nonrecurring [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Assets, Fair Value Disclosure, Nonrecurring		24,000	91,000
Assets Held-for-sale [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) | Fair Value, Measurements, Nonrecurring [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Assets, Fair Value Disclosure, Nonrecurring		0	0
Assets Held-for-sale [Member] | Significant Other Observable Inputs (Level 2) | Fair Value, Measurements, Nonrecurring [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Assets, Fair Value Disclosure, Nonrecurring		$ 0	$ 0
Assets Held-for-sale [Member] | Significant Unobservable Inputs (Level 3) | Minimum [Member] | Third Party Valuations [Member]
Assets Measured On Recurring And Nonrecurring Basis Valuation Techniques [Abstract]
Discount to reflect realizable value less estimated selling costs (in hundredths)		0.00%	0.00%
Assets Held-for-sale [Member] | Significant Unobservable Inputs (Level 3) | Maximum [Member] | Third Party Valuations [Member]
Assets Measured On Recurring And Nonrecurring Basis Valuation Techniques [Abstract]
Discount to reflect realizable value less estimated selling costs (in hundredths)		40.00%	40.00%
Assets Held-for-sale [Member] | Significant Unobservable Inputs (Level 3) | Weighted Average [Member] | Third Party Valuations [Member]
Assets Measured On Recurring And Nonrecurring Basis Valuation Techniques [Abstract]
Discount to reflect realizable value less estimated selling costs (in hundredths)		35.00%	35.00%
Assets Held-for-sale [Member] | Significant Unobservable Inputs (Level 3) | Fair Value, Measurements, Nonrecurring [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Assets, Fair Value Disclosure, Nonrecurring		$ 24,000	$ 91,000

[1] Every five years