EMPLOYEE BENEFITS - Narrative (Details)	12 Months Ended
	Dec. 31, 2018 USD ($) executive_officer Rate shares	Dec. 31, 2017 USD ($) shares	Dec. 31, 2016 USD ($) executive_officer shares	Dec. 31, 2015	Dec. 31, 2013 executive_officer
Health Insurance Coverage [Abstract]
Cost of health care benefits	$ 6,500,000	$ 5,600,000	$ 4,900,000
Health coverage eligibility for retiring employees, minimum years of service	50 years
Retirees participating in health insurance	1	2	2
Employee Stock Ownership Plan (ESOP) [Abstract]
Contributions to the employee stock ownership plan (ESOP)	$ 700,000	$ 350,000	$ 350,000
Shares owned by the ESOP (in shares) | shares	277,492	280,542
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
Long-term disability coverage, maximum benefit provided, as a ratio of final salary | Rate	66.66667%
401(k) [Abstract]
Requisite service period	30 days
401(k) Plan expense	$ 1,500,000	$ 613,000	562,000
Share-based Compensation [Abstract]
Tax benefit (expense) realized for deductions related to stock option exercises			332,000
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
Number of shares of Company stock included in plan assets (in shares) | shares	240,666	240,666
Funded (under funded) status	$ (1,081,000)	$ (3,043,000)	$ (2,778,000)
Number of employees offered early retirement			24
Total number of employees that accepted early retirement offer			15	16
Special and contractual termination benefits	0	0	$ 1,549,000
Accrued benefit (liability) asset recognized	(1,081,000)	(3,043,000)	(2,778,000)
Expected future employer contributions, next fiscal year	0
Defined Benefit Pension Plan Acquired
Defined Benefit Plan [Abstract]
Funded (under funded) status	197,000	(361,000)	(1,245,000)
Special and contractual termination benefits	0	0	0
Accrued benefit (liability) asset recognized	197,000	(361,000)	(1,245,000)
Expected future employer contributions, next fiscal year	0
Restoration Plan
Defined Benefit Plan [Abstract]
Funded (under funded) status	(15,300,000)	(14,642,000)	(12,723,000)
Special and contractual termination benefits	0	0	0
Accrued benefit (liability) asset recognized	(15,300,000)	$ (14,642,000)	$ (12,723,000)
Expected future employer contributions, next fiscal year	$ 0
Other 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 Compensation [Abstract]
Nonvested awards outstanding (in shares) | shares	109,750	78,253
Incentive Plan 2009
Share-based Compensation [Abstract]
Number of additional shares (in shares) | shares	410,000
Incentive Plan 2017
Share-based Compensation [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	1,675,607
Incentive Plan
Share-based Compensation [Abstract]
Nonvested awards outstanding (in shares) | shares	612,740	366,292	599,498
Share-based compensation expense	$ 2,300,000	$ 1,800,000	$ 1,500,000
Tax benefit from share-based compensation expense	487,000	635,000	539,000
Unrecognized compensation expense	$ 5,800,000	3,800,000	5,600,000
Unrecognized compensation, weighted-average period for recognition	2 years 9 months 14 days
Incentive Plan | Stock options
Share-based Compensation [Abstract]
Awards contractual term	10 years
Total intrinsic value of outstanding stock options	$ 3,700,000
Total intrinsic value of exercisable stock options	$ 3,200,000
Weighted-average remaining contractual life of options exercisable	5 years 5 months 28 days
Total intrinsic value of stock options exercised during period	$ 1,400,000	1,800,000	1,300,000
Tax benefit (expense) realized for deductions related to stock option exercises	$ 0	0	$ 332,000
Incentive Plan | Stock options | Minimum
Share-based Compensation [Abstract]
Awards vesting period	3 years
Incentive Plan | Stock options | Maximum
Share-based Compensation [Abstract]
Awards vesting period	4 years
Incentive Plan | Restricted Stock Units (RSUs) | Minimum
Share-based Compensation [Abstract]
Awards vesting period	3 years
Incentive Plan | Restricted Stock Units (RSUs) | Maximum
Share-based Compensation [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	17
Aggregate payment amount provided in the deferred compensation agreements	$ 6,900,000
Maximum benefit period after retirement or death	15 years
Number of individuals receiving payments | executive_officer	9
Number of individuals that accepted the retirement package | executive_officer			3
Deferred compensation expense	$ 201,000	353,000	$ 357,000
Total deferred compensation plan liability	$ 3,400,000	3,500,000
Split Dollar Life Insurance Agreements [Abstract]
Number of employees originally covered by the split dollar agreements | executive_officer	8
Aggregate death benefit amount provided 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, inflation adjusted	$ 4,100,000
Expense of split dollar retirement bonus	(250,000)	(3,000)	$ 172,000
Total split dollar liability	$ 1,400,000	$ 1,900,000
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%