BENEFIT PLANS, Funded Status and Amounts Recognized in Balance Sheets and AOCI (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2009
Change in plan assets [Roll Forward]
Fair value of plan assets at beginning of year	[1]	$ 177,551
Fair value of plan assets at end of year	[1]	171,625	$ 177,551
Amounts recognized in accumulated other comprehensive income (loss) (AOCI) [Abstract]
AOCI at year end		21,283	16,716	$ 7,145
Accumulated other comprehensive income (loss), negative postretirement medical plan amendment, arising during period, net of tax					$ 3,500
Pension Benefits [Member]
Change in benefit obligation [Roll Forward]
Benefit obligation at the beginning of year		127,513	111,174
Service cost		3,324	3,530	3,988
Interest cost		5,506	5,271	4,120
Plan acquisition / amendment		2,395	2,091
Participant contributions		0	0
Deferred actuarial (gain)/loss		(2,091)	13,005
Benefits paid		(9,513)	(7,558)
Benefit obligation at end of year		127,134	127,513	111,174
Change in plan assets [Roll Forward]
Fair value of plan assets at beginning of year		177,865	173,416
Actual return of plan assets		1,125	11,391
Participant contributions		0	0
Employer contributions		616	616
Plan acquisition		1,933	0
Benefits paid		(9,513)	(7,558)
Fair value of plan assets at end of year		172,026	177,865	173,416
Defined Benefit Plan, Funded Status of Plan [Abstract]
Over/(Under) funded status at year end		44,892	50,352
Amounts recognized in the consolidated statement of condition [Abstract]
Other assets		56,361	61,437
Other liabilities		(11,469)	(11,085)
Amounts recognized in accumulated other comprehensive income (loss) (AOCI) [Abstract]
Net loss		34,016	26,748
Net prior service cost (credit)		2,307	2,316
Pre-tax AOCI		36,323	29,064
Taxes		(13,815)	(11,033)
AOCI at year end		22,508	18,031
Post-retirement Benefits [Member]
Change in benefit obligation [Roll Forward]
Benefit obligation at the beginning of year		2,256	2,340
Service cost		0	0	0
Interest cost		87	102	88
Plan acquisition / amendment		0	0
Participant contributions		509	551
Deferred actuarial (gain)/loss		(45)	55
Benefits paid		(889)	(792)
Benefit obligation at end of year		1,918	2,256	2,340
Change in plan assets [Roll Forward]
Fair value of plan assets at beginning of year		0	0
Actual return of plan assets		0	0
Participant contributions		509	551
Employer contributions		380	241
Plan acquisition		0	0
Benefits paid		(889)	(792)
Fair value of plan assets at end of year		0	0	$ 0
Defined Benefit Plan, Funded Status of Plan [Abstract]
Over/(Under) funded status at year end		(1,918)	(2,256)
Amounts recognized in the consolidated statement of condition [Abstract]
Other assets		0	0
Other liabilities		(1,918)	(2,256)
Amounts recognized in accumulated other comprehensive income (loss) (AOCI) [Abstract]
Net loss		4	36
Net prior service cost (credit)		(1,980)	(2,159)
Pre-tax AOCI		(1,976)	(2,123)
Taxes		751	808
AOCI at year end		(1,225)	(1,315)
Unfunded Supplementary Pension Plans [Member]
Change in benefit obligation [Roll Forward]
Benefit obligation at the beginning of year		11,000
Benefit obligation at end of year		11,400	11,000
Amounts recognized in accumulated other comprehensive income (loss) (AOCI) [Abstract]
Benefit obligation for defined benefit pension plan prior to plan revaluation		115,700	116,400
Unfunded Stock Balance [Member] | Nonemployee Directors [Member]
Change in benefit obligation [Roll Forward]
Benefit obligation at the beginning of year		100
Benefit obligation at end of year		$ 100	$ 100

[1] Excludes dividends and interest receivable totaling $0.4 million and $0.3 million at December 31, 2015 and 2014, respectively.