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Fair Value of Assets and Liabilities, Part II (Details) - USD ($)	3 Months Ended	12 Months Ended
	Mar. 31, 2019	Dec. 31, 2018
Foreclosed Assets Held for Sale [Abstract]
Other real estate owned	$ 3,796,000	$ 2,534,000
Financial Assets [Abstract]
Available-for-sale securities	695,618,000	692,274,000
Debt Securities, Held-to-maturity	69,462,000	69,436,000
Debt Securities, Held-to-maturity, Fair Value	68,743,000	67,909,000
Operating lease right-of-use assets	13,531,000	0
Financial Liabilities [Abstract]
Operating lease liabilities	13,533,000	0
Carrying Amount [Member]
Financial Assets [Abstract]
Cash and due from banks	232,052,000	140,735,000
Federal funds sold	496,000	665,000
Certificates of deposit investments	7,320,000.000	7,569,000.000
Available-for-sale securities	695,618,000	692,274,000
Debt Securities, Held-to-maturity	69,462,000	69,436,000
Loans held for sale	1,233,000	1,508,000
Loans net of allowance for loan losses	2,569,057,000	2,616,822,000
Interest receivable	16,073,000	16,881,000
Operating lease right-of-use assets	13,531,000
Federal Reserve Bank stock	7,389,000	7,390,000
Federal Home Loan Bank stock	2,995,000	3,095,000
Financial Liabilities [Abstract]
Deposits	3,046,213,000	2,988,686,000
Securities sold under agreements to repurchase	157,760,000	192,330,000
Interest payable	2,166,000	1,758,000
Federal Home Loan Bank borrowings	119,791,000	119,745,000
Other borrowings	6,257,000	7,724,000
Junior subordinated debentures	29,042,000	29,000,000
Operating lease liabilities	13,533,000
Fair Value [Member]
Financial Assets [Abstract]
Cash and due from banks	232,052,000	140,735,000
Federal funds sold	496,000	665,000
Certificates of deposit investments	7,320,000.000	7,569,000.000
Available-for-sale securities	695,618,000	692,274,000
Debt Securities, Held-to-maturity, Fair Value	68,743,000	67,909,000
Loans held for sale	1,233,000	1,508,000
Loans net of allowance for loan losses	2,520,206,000	2,541,037,000
Interest receivable	16,073,000	16,881,000
Operating lease right-of-use assets	13,531,000
Federal Reserve Bank stock	7,389,000	7,390,000
Federal Home Loan Bank stock	2,995,000	3,095,000
Financial Liabilities [Abstract]
Deposits	3,051,083,000	2,991,177,000
Securities sold under agreements to repurchase	157,647,000	192,179,000
Interest payable	2,166,000	1,758,000
Federal Home Loan Bank borrowings	120,079,000	119,704,000
Other borrowings	6,257,000	7,724,000
Junior subordinated debentures	24,302,000	24,418,000
Operating lease liabilities	13,533,000
Fair Value, Measurements, Nonrecurring [Member] | Carrying Amount [Member]
Foreclosed Assets Held for Sale [Abstract]
Other real estate owned	3,796,000
Fair Value, Measurements, Nonrecurring [Member] | Fair Value [Member]
Foreclosed Assets Held for Sale [Abstract]
Other real estate owned	1,574,000
Quoted Prices in Active Markets for Identical Assets (Level 1)
Financial Assets [Abstract]
Cash and due from banks	232,052,000	140,735,000
Federal funds sold	496,000	665,000
Available-for-sale securities	96,000	364,000
Debt Securities, Held-to-maturity, Fair Value	0	0
Loans held for sale	0	0
Loans net of allowance for loan losses	0	0
Interest receivable	0	0
Operating lease right-of-use assets	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
Operating lease liabilities	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	7,320,000.000	7,569,000.000
Available-for-sale securities	694,554,000	690,943,000
Debt Securities, Held-to-maturity, Fair Value	68,743,000	67,909,000
Loans held for sale	1,233,000	1,508,000
Loans net of allowance for loan losses	0	0
Interest receivable	16,073,000	16,881,000
Operating lease right-of-use assets	13,531,000
Federal Reserve Bank stock	7,389,000	7,390,000
Federal Home Loan Bank stock	2,995,000	3,095,000
Financial Liabilities [Abstract]
Deposits	2,385,575,000	2,396,917,000
Securities sold under agreements to repurchase	157,647,000	192,179,000
Interest payable	2,166,000	1,758,000
Federal Home Loan Bank borrowings	120,079,000	119,704,000
Other borrowings	6,257,000	7,724,000
Junior subordinated debentures	24,302,000	24,418,000
Operating lease liabilities	13,533,000
Significant Unobservable Inputs (Level 3)
Financial Assets [Abstract]
Cash and due from banks	0	0
Federal funds sold	0	0
Available-for-sale securities	968,000	967,000
Debt Securities, Held-to-maturity, Fair Value	0	0
Loans held for sale	0	0
Loans net of allowance for loan losses	2,520,206,000	2,541,037,000
Interest receivable	0	0
Operating lease right-of-use assets	0
Federal Reserve Bank stock	0	0
Federal Home Loan Bank stock	0	0
Financial Liabilities [Abstract]
Deposits	665,508,000	594,260,000
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
Operating lease liabilities	0
Impaired loans (collateral dependent) | Fair Value, Measurements, Nonrecurring [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Assets, Fair Value Disclosure	8,478,000	16,437,000
Impaired loans (collateral dependent) | Quoted Prices in Active Markets for Identical Assets (Level 1) | Fair Value, Measurements, Nonrecurring [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Assets, Fair Value Disclosure	0	0
Impaired loans (collateral dependent) | Significant Other Observable Inputs (Level 2) | Fair Value, Measurements, Nonrecurring [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Assets, Fair Value Disclosure	$ 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 Measurement Inputs and Valuation Techniques [Line Items]
Assets, Fair Value Disclosure	$ 8,478,000	$ 16,437,000
Assets Held-for-sale [Member] | Fair Value, Measurements, Nonrecurring [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Assets, Fair Value Disclosure	1,574,000	836,000
Assets Held-for-sale [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) | Fair Value, Measurements, Nonrecurring [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Assets, Fair Value Disclosure	0	0
Assets Held-for-sale [Member] | Significant Other Observable Inputs (Level 2) | Fair Value, Measurements, Nonrecurring [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Assets, Fair Value Disclosure	$ 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 Measurement Inputs and Valuation Techniques [Line Items]
Assets, Fair Value Disclosure	$ 1,574,000	$ 836,000

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