EMPLOYEE BENEFITS - Narrative (Details)	3 Months Ended		6 Months Ended	12 Months Ended
	Jun. 30, 2020 USD ($)	Mar. 31, 2020	Jun. 30, 2020 USD ($)	Dec. 31, 2020 USD ($) executive_officer shares	Dec. 31, 2019 USD ($) shares	Dec. 31, 2018 USD ($) executive_officer shares	Dec. 31, 2013 executive_officer	Jun. 29, 2020
Health Insurance Coverage [Abstract]
Cost of health care benefits				$ 7,000,000.0	$ 7,900,000	$ 6,500,000
Health coverage eligibility for retiring employees, minimum years of service				50 years
Retirees participating in health insurance				1	1	1
Employee Stock Ownership Plan (ESOP) [Abstract]
Contributions to the employee stock ownership plan (ESOP)				$ 1,000,000.0	$ 700,000	$ 700,000
Shares owned by the ESOP (in shares) | shares				323,606	283,097
Supplemental Unemployment Benefits [Abstract]
Long-term disability coverage, minimum years of service rendered for officers to automatically qualify				3 years
Long-term disability coverage, minimum annual salary level for officers to automatically qualify				$ 50,000
Long-term disability coverage, maximum benefit provided, per month				$ 15,000
401(k) [Abstract]
Requisite service period				30 days
401(k) Plan expense				$ 1,900,000	$ 1,600,000	1,500,000
Defined Benefit Plan [Abstract]
Retirement plan curtailment expense			$ 163,000	163,000	0	0
Decrease in accumulated other comprehensive income due to freeze of future benefits and remeasurement	$ 6,000,000.0		$ 6,000,000.0
Non-cash adjustment to pension plan liabilities, consisting of changes in prior service cost and net loss				$ 2,800,000
Defined Benefit Pension Plan
Defined Benefit Plan [Abstract]
Defined benefit pension plan, minimum eligibility age				65 years
Early retirement election at reduced benefit levels, minimum eligibility age				55 years
Retirement plan curtailment expense				$ 151,000	$ 0	$ 0
Discount rate	2.78%		2.78%	2.65%	3.41%			3.41%
Number of shares of Company stock included in plan assets (in shares) | shares				240,666	240,666
Expected long-term rate of return on plan assets	6.50%	7.25%		6.50%	7.25%	7.25%
Funded (under funded) status				$ (6,429,000)	$ (6,194,000)	$ (1,081,000)
Accrued benefit (liability) asset recognized				(6,429,000)	(6,194,000)	(1,081,000)
Expected future employer contributions, next fiscal year				0
Defined Benefit Pension Plan Acquired
Defined Benefit Plan [Abstract]
Retirement plan curtailment expense				$ 0	$ 0	$ 0
Discount rate				2.65%	3.41%
Expected long-term rate of return on plan assets	6.50%	7.25%		6.50%	7.25%	7.25%
Funded (under funded) status				$ (91,000)	$ (107,000)	$ 197,000
Accrued benefit (liability) asset recognized				(91,000)	(107,000)	197,000
Expected future employer contributions, next fiscal year				0
Restoration Plan
Defined Benefit Plan [Abstract]
Retirement plan curtailment expense				$ 12,000	$ 0	0
Discount rate	2.78%		2.78%	2.65%	3.41%			3.41%
Funded (under funded) status				$ (18,789,000)	$ (19,098,000)	(15,300,000)
Accrued benefit (liability) asset recognized				(18,789,000)	$ (19,098,000)	$ (15,300,000)
Expected future employer contributions, next fiscal year				$ 918,000
Equity securities | Defined Benefit Pension Plan
Defined Benefit Plan [Abstract]
Target allocation				55.00%
Fixed income securities | Defined Benefit Pension Plan
Defined Benefit Plan [Abstract]
Target allocation				44.50%
Cash equivalents | Defined Benefit Pension Plan
Defined Benefit Plan [Abstract]
Target allocation				0.50%
Restricted Stock Units (RSUs)
Share-based Payment Arrangement, Noncash Expense [Abstract]
Nonvested awards outstanding (in shares) | shares				123,694	143,291
Incentive Plan 2009
Share-based Payment Arrangement, Noncash Expense [Abstract]
Number of additional shares (in shares) | shares				410,000
Incentive Plan 2017
Share-based Payment Arrangement, Noncash Expense [Abstract]
Common stock shares reserved and available for issuance (in shares) | shares				2,460,000
Shares remaining available for grant for future awards (in shares) | shares				1,302,958
Incentive Plan
Share-based Payment Arrangement, Noncash Expense [Abstract]
Nonvested awards outstanding (in shares) | shares				492,274	737,434	612,740
Share-based compensation expense				$ 2,800,000	$ 2,400,000	$ 2,300,000
Tax benefit from share-based compensation expense				593,000	501,000	487,000
Unrecognized compensation expense				$ 5,400,000	7,700,000	5,800,000
Unrecognized compensation, weighted-average period for recognition				2 years 3 months 18 days
Incentive Plan | Stock options
Share-based Payment Arrangement, Noncash Expense [Abstract]
Total intrinsic value of outstanding stock options				$ 1,900,000
Total intrinsic value of exercisable stock options				$ 1,900,000
Weighted-average remaining contractual life of options exercisable				5 years 7 months 6 days
Awards contractual term				10 years
Incentive Plan | Stock options | Minimum
Share-based Payment Arrangement, Noncash Expense [Abstract]
Awards vesting period				3 years
Incentive Plan | Stock options | Maximum
Share-based Payment Arrangement, Noncash Expense [Abstract]
Awards vesting period				4 years
Incentive Plan | Restricted Stock Units (RSUs) | Minimum
Share-based Payment Arrangement, Noncash Expense [Abstract]
Awards vesting period				3 years
Incentive Plan | Restricted Stock Units (RSUs) | Maximum
Share-based Payment Arrangement, Noncash Expense [Abstract]
Awards vesting period				4 years
Executive officers
Deferred Compensation Arrangements [Abstract]
Number of employees included in the deferred compensation agreement with the Company | executive_officer				33
Aggregate payment amount provided in the deferred compensation agreements				$ 11,000,000.0
Maximum benefit period after retirement or death				15 years
Number of individuals receiving payments | executive_officer				10
Deferred compensation expense				$ 667,000	173,000	$ 201,000
Total deferred compensation plan liability				$ 3,500,000	3,200,000
Split Dollar Life Insurance Agreements [Abstract]
Number of employees originally covered by the split dollar agreements | executive_officer				8
Aggregate death benefit amount provided originally in agreement, before inflation adjustment				$ 4,500,000
Number of employees covered by the split dollar agreements, Actively employed with us | executive_officer				3
Number of retired covered officers death benefits were paid | executive_officer						1
Number of active covered officers death benefits were paid | executive_officer							1
Number of remaining employees covered by the split dollar agreements | executive_officer				6
Aggregate death benefits for remaining six executives, inflation adjusted				$ 4,500,000
(Expense) Credit to expense of Split Dollar Retirement Bonus				(35,000)	12,000	$ 250,000
Total split dollar liability				$ 1,500,000	$ 1,300,000
Executive officers | Minimum
Split Dollar Life Insurance Agreements [Abstract]
Inflation adjustment factor applied to benefits, annual				3.00%
Executive officers | Maximum
Split Dollar Life Insurance Agreements [Abstract]
Inflation adjustment factor applied to benefits, annual				5.00%