PENSION AND OTHER BENEFIT PLANS - Funded status and amounts recognized in balance sheets and AOCI (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2009
Amounts recognized in accumulated other comprehensive loss/(income) ("AOCI") were:
AOCI at year end	$ 31,301	$ 15,470	$ 28,873
Accumulated other comprehensive income (loss), negative postretirement medical plan amendment, arising during period, net of tax				$ 3,500
Pension Benefits
Change in benefit obligation:
Benefit obligation at the beginning of year	183,270	190,361
Service cost	4,959	5,920	5,750
Interest cost	5,334	5,036	5,657
Plan amendment / acquisition	1,851	0
Participant contributions	0	0
Deferred actuarial (gain)/loss	(31,759)	(4,881)
Benefits paid	(12,294)	(13,166)
Benefit obligation at end of year	151,361	183,270	190,361
Change in plan assets:
Fair value of plan assets at beginning of year	290,687	272,600
Actual return of plan assets	(34,967)	27,614
Participant contributions	0	0
Employer contributions	906	3,639
Plan acquisition	0	0
Benefits paid	(12,294)	(13,166)
Fair value of plan assets at end of year	244,332	290,687	272,600
Over/(Under) funded status at year end	92,971	107,417
Amounts recognized in the consolidated statement of condition were:
Other assets	106,986	127,538
Other liabilities	(14,015)	(20,121)
Amounts recognized in accumulated other comprehensive loss/(income) ("AOCI") were:
Net loss	38,894	16,977
Net prior service cost (credit)	3,112	3,969
Pre-tax AOCI	42,006	20,946
Taxes	(10,351)	(5,236)
AOCI at year end	31,655	15,710
Pension Benefits | Nonqualified Plan | Unfunded Plan
Change in plan assets:
Employer contributions	100	2,900
Pension Benefits | Restoration Plan | Nonqualified Plan | Unfunded Plan
Amounts recognized in accumulated other comprehensive loss/(income) ("AOCI") were:
Initial projected benefit obligation		300
Post-retirement Benefits
Change in benefit obligation:
Benefit obligation at the beginning of year	1,529	1,718
Service cost	0	0	0
Interest cost	68	44	57
Plan amendment / acquisition	536	0
Participant contributions	0	0
Deferred actuarial (gain)/loss	(306)	(85)
Benefits paid	(171)	(148)
Benefit obligation at end of year	1,656	1,529	1,718
Change in plan assets:
Fair value of plan assets at beginning of year	0	0
Actual return of plan assets	0	0
Participant contributions	0	0
Employer contributions	171	148
Plan acquisition	0	0
Benefits paid	(171)	(148)
Fair value of plan assets at end of year	0	0	$ 0
Over/(Under) funded status at year end	(1,656)	(1,529)
Amounts recognized in the consolidated statement of condition were:
Other assets	0	0
Other liabilities	(1,656)	(1,529)
Amounts recognized in accumulated other comprehensive loss/(income) ("AOCI") were:
Net loss	255	585
Net prior service cost (credit)	(728)	(907)
Pre-tax AOCI	(473)	(322)
Taxes	119	82
AOCI at year end	$ (354)	(240)
Supplemental Pension Plans | Key Executives
Pension Plans
Defined Benefit Plan, Funding Status [Extensible List]	Unfunded Plan
Change in benefit obligation:
Benefit obligation at the beginning of year	$ 19,800
Benefit obligation at end of year	14,000	19,800
Amounts recognized in accumulated other comprehensive loss/(income) ("AOCI") were:
Benefit obligation for defined benefit pension plan prior to plan revaluation	$ 137,300	$ 163,100