FAIR VALUE OF FINANCIAL ASSETS AND LIABILITIES (Schedule of Carrying Amount and Estimated Fair Value of Financial Instruments) (Details) - USD ($)	3 Months Ended
	Mar. 31, 2018	Dec. 31, 2017	Mar. 31, 2017	Dec. 31, 2016
Financial assets
Cash and due from banks	$ 59,905,000	$ 75,318,000
Interest-bearing deposits in other banks	5,875,000	6,975,000
Loans held for sale	7,492,000	16,336,000
Mortgage servicing rights	15,821,000	15,843,000
Federal Home Loan Bank stock	9,007,000	7,761,000
Accrued interest receivable	16,070,000	16,581,000
Deposits:
Noninterest-bearing deposits	1,349,029,000	1,395,556,000
Time deposits	1,151,455,000	1,145,868,000
Transfers of financial assets from Level 1 to Level 2	0
Transfers of financial assets from Level 2 to Level 1	0
Transfers of financial liabilities from Level 1 to Level 2	0
Transfers of financial liabilities from Level 2 to Level 1	0
Transfers of financial assets out of Level 3	0
Transfers of financial liabilities out of Level 3	0
Carrying Amount
Financial assets
Cash and due from banks	59,905,000	75,318,000
Interest-bearing deposits in other banks	5,875,000	6,975,000
Investment securities	1,503,923,000	1,496,644,000
Loans held for sale	7,492,000	16,336,000
Net loans and leases	3,766,929,000	3,720,614,000
Mortgage servicing rights	15,821,000	15,843,000
Federal Home Loan Bank stock	9,007,000	7,761,000
Accrued interest receivable	16,070,000	16,581,000
Deposits:
Noninterest-bearing deposits	1,349,029,000	1,395,556,000
Interest-bearing demand and savings deposits	2,479,947,000	2,414,930,000
Time deposits	1,151,455,000	1,145,868,000
Short-term debt	56,000,000	32,000,000
Long-term debt	92,785,000	92,785,000
Accrued interest payable (included in other liabilities)	3,809,000	3,698,000
Carrying Amount | Commitments to extend credit
Deposits:
Off-balance sheet financial instruments	961,167,000	917,405,000
Carrying Amount | Standby letters of credit and financial guarantees written
Deposits:
Off-balance sheet financial instruments	12,108,000	13,551,000
Carrying Amount | Interest rate lock commitments
Deposits:
Off-balance sheet financial instruments	3,126,000	2,494,000
Carrying Amount | Forward sale commitments
Deposits:
Off-balance sheet financial instruments	9,172,000	18,748,000
Estimated Fair Value
Financial assets
Cash and due from banks	59,905,000	75,318,000
Interest-bearing deposits in other banks	5,875,000	6,975,000
Investment securities	1,498,244,000	1,494,092,000
Loans held for sale	7,492,000	16,336,000
Net loans and leases	3,706,552,000	3,684,834,000
Mortgage servicing rights	18,463,000	17,161,000
Federal Home Loan Bank stock	9,007,000	7,761,000
Accrued interest receivable	16,070,000	16,581,000
Deposits:
Noninterest-bearing deposits	1,349,029,000	1,395,556,000
Interest-bearing demand and savings deposits	2,479,947,000	2,414,930,000
Time deposits	1,144,494,000	1,140,064,000
Short-term debt	56,000,000	32,000,000
Long-term debt	87,923,000	70,139,000
Accrued interest payable (included in other liabilities)	3,809,000	3,698,000
Estimated Fair Value | Commitments to extend credit
Deposits:
Off-balance sheet financial instruments	1,183,000	1,140,000
Estimated Fair Value | Standby letters of credit and financial guarantees written
Deposits:
Off-balance sheet financial instruments	182,000	203,000
Estimated Fair Value | Interest rate lock commitments
Deposits:
Off-balance sheet financial instruments	13,000	12,000
Estimated Fair Value | Forward sale commitments
Deposits:
Off-balance sheet financial instruments	(6,000)	(26,000)
Quoted Prices in Active Markets for Identical Assets (Level 1)
Financial assets
Cash and due from banks	59,905,000	75,318,000
Interest-bearing deposits in other banks	5,875,000	6,975,000
Investment securities	753,000	825,000
Loans held for sale	0	0
Net loans and leases	0	0
Mortgage servicing rights	0	0
Federal Home Loan Bank stock	9,007,000	7,761,000
Accrued interest receivable	16,070,000	16,581,000
Deposits:
Noninterest-bearing deposits	1,349,029,000	1,395,556,000
Interest-bearing demand and savings deposits	2,479,947,000	2,414,930,000
Time deposits	0	0
Short-term debt	0	0
Long-term debt	0	0
Accrued interest payable (included in other liabilities)	3,809,000	3,698,000
Quoted Prices in Active Markets for Identical Assets (Level 1) | Commitments to extend credit
Deposits:
Off-balance sheet financial instruments	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Standby letters of credit and financial guarantees written
Deposits:
Off-balance sheet financial instruments	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Interest rate lock commitments
Deposits:
Off-balance sheet financial instruments	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Forward sale commitments
Deposits:
Off-balance sheet financial instruments	0	0
Significant Other Observable Inputs (Level 2)
Financial assets
Cash and due from banks	0	0
Interest-bearing deposits in other banks	0	0
Investment securities	1,485,953,000	1,481,473,000
Loans held for sale	7,492,000	16,336,000
Net loans and leases	20,963,000	21,280,000
Mortgage servicing rights	0	0
Federal Home Loan Bank stock	0	0
Accrued interest receivable	0	0
Deposits:
Noninterest-bearing deposits	0	0
Interest-bearing demand and savings deposits	0	0
Time deposits	0	0
Short-term debt	56,000,000	32,000,000
Long-term debt	87,923,000	70,139,000
Accrued interest payable (included in other liabilities)	0	0
Significant Other Observable Inputs (Level 2) | Commitments to extend credit
Deposits:
Off-balance sheet financial instruments	1,183,000	1,140,000
Significant Other Observable Inputs (Level 2) | Standby letters of credit and financial guarantees written
Deposits:
Off-balance sheet financial instruments	182,000	203,000
Significant Other Observable Inputs (Level 2) | Interest rate lock commitments
Deposits:
Off-balance sheet financial instruments	13,000	12,000
Significant Other Observable Inputs (Level 2) | Forward sale commitments
Deposits:
Off-balance sheet financial instruments	(6,000)	(26,000)
Significant Unobservable Inputs (Level 3)
Financial assets
Cash and due from banks	0	0
Interest-bearing deposits in other banks	0	0
Investment securities	11,538,000	11,794,000
Loans held for sale	0	0
Net loans and leases	3,685,589,000	3,663,554,000
Mortgage servicing rights		17,161,000
Federal Home Loan Bank stock	0	0
Accrued interest receivable	0	0
Deposits:
Noninterest-bearing deposits	0	0
Interest-bearing demand and savings deposits	0	0
Time deposits	1,144,494,000	1,140,064,000
Short-term debt	0	0
Long-term debt	0	0
Accrued interest payable (included in other liabilities)	0	0
Significant Unobservable Inputs (Level 3) | Commitments to extend credit
Deposits:
Off-balance sheet financial instruments	0	0
Significant Unobservable Inputs (Level 3) | Standby letters of credit and financial guarantees written
Deposits:
Off-balance sheet financial instruments	0	0
Significant Unobservable Inputs (Level 3) | Interest rate lock commitments
Deposits:
Off-balance sheet financial instruments	0	0
Significant Unobservable Inputs (Level 3) | Forward sale commitments
Deposits:
Off-balance sheet financial instruments	0	0
Mortgage Servicing Rights
Financial assets
Finite-lived Intangible Assets, Fair Value Disclosure	$ 18,463,000	$ 17,161,000	$ 17,627,000	$ 18,087,000