LOANS AND ALLOWANCE FOR CREDIT LOSSES ON LOANS (Narrative) (Details)	3 Months Ended			6 Months Ended
	Jun. 30, 2021 USD ($) loan	Mar. 31, 2021 USD ($) loan	Jun. 30, 2020 USD ($) loan	Jun. 30, 2021 USD ($) loan	Jun. 30, 2020 USD ($) loan	Dec. 31, 2020 USD ($)
Accounts, Notes, Loans and Financing Receivable [Line Items]
SBA PPP Loans, Total Originations, Number of Loans | loan		3,034		1,620
SBA PPP Loans, Total Originations		$ 244,800,000		$ 102,200,000
Loans and Leases Receivable, Related Parties, Description		At June 30, 2021 and December 31, 2020, outstanding loans to certain officers, directors and their associated companies was less than 5% of the Company's shareholders' equity.		At June 30, 2021 and December 31, 2020, outstanding loans to certain officers, directors and their associated companies was less than 5% of the Company's shareholders' equity.
Proceeds from the sale of mortgage loans				$ 312,474,000	$ 176,250,000
Gain on sale of mortgage loans				(9,084,000)	(6,095,000)
Loans held for sale, at fair value (book value of $14,887 and $40,499, respectively)	$ 15,140,000			$ 15,140,000		$ 41,557,000
Allowance for Loan and Lease Losses, Period Increase (Decrease)	5,800,000		$ (32,100,000)
Other industry exposures				0
Temporary Loan Modifications, COVID-Related Loan Modification, Recorded Investment	0			$ 0		26,500,000
Non-Accrual Loans	5,882,000			5,882,000		7,596,000
Loans outstanding	3,285,916,000			3,285,916,000		3,219,822,000
Interest lost on nonaccrual loans	67,000		$ 87,000	143,000	$ 166,000
Loans and Leases Receivable, Excluded Accrued Interest from Amortized Cost	8,600,000			8,600,000		10,200,000
Recorded Investment	2,826,000			2,826,000		3,066,000
Financing Receivable, Troubled Debt Restructuring, Commitment to Lend	$ 0			$ 0		0
Loans modified | loan	0		0	0	0
FHLB advances, general debt obligations, pledged collateral	$ 1,300,000,000			$ 1,300,000,000		1,300,000,000
CARES Act
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-Accrual Loans	1,300,000			1,300,000		457,000
CARES Act | 30 to 89 days past due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans outstanding	536,000			536,000		1,200,000
SBA PPP Portfolio Segment
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans outstanding	126,064,000			126,064,000		135,095,000
Residential Real Estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-Accrual Loans	2,725,000			2,725,000		3,477,000
Loans outstanding	1,120,917,000			1,120,917,000		1,054,798,000
Mortgage Loans in Process of Foreclosure, Amount	1,300,000			1,300,000		1,500,000
Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-Accrual Loans	1,511,000			1,511,000		1,607,000
Loans outstanding	367,093,000			367,093,000		381,494,000
Home Equity
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-Accrual Loans	1,396,000			1,396,000		1,996,000
Loans outstanding	228,690,000			228,690,000		258,573,000
Consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-Accrual Loans	28,000			28,000		4,000
Loans outstanding	19,255,000			19,255,000		20,392,000
Fixed Rate Residential Mortgage
Accounts, Notes, Loans and Financing Receivable [Line Items]
Proceeds from the sale of mortgage loans	110,800,000		$ 197,800,000	303,400,000	$ 267,000,000.0
Gain on sale of mortgage loans	(2,900,000)		(4,600,000)	(9,100,000)	(6,100,000)
Loans held for sale, at fair value (book value of $14,887 and $40,499, respectively)	14,900,000			14,900,000		40,500,000
Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Recorded Investment	89,000			89,000		100,000
Nonoperating Income (Expense) | Fixed Rate Residential Mortgage
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gain on sale of mortgage loans	(267,000)		(1,300,000)	$ 804,000	$ (742,000)
Unrealized gain (loss) on loans held for sale	253,000		$ 1,100,000
Non-Residential Building Operators Industry Sector | Loan Concentration Risk | Total Loan Portfolio
Accounts, Notes, Loans and Financing Receivable [Line Items]
Concentration risk (percentage)				14.00%
Non-Residential Building Operators Industry Sector | Loan Concentration Risk | Commercial Real Estate(1)
Accounts, Notes, Loans and Financing Receivable [Line Items]
Concentration risk (percentage)				32.00%
Performing Financial Instruments [Member] | Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Recorded Investment	2,500,000			$ 2,500,000		2,800,000
Nonperforming Financial Instruments [Member] | Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Recorded Investment	$ 306,000			$ 306,000		$ 248,000