OTHER COMPREHENSIVE INCOME (LOSS) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Other Comprehensive Income (Loss) [Abstract]
Tax expense (benefit)	$ 8,241	$ 7,092	$ 7,987	$ 7,925	$ 7,628	$ 7,788	$ 7,531	$ 7,177	$ 31,245	$ 30,124	$ 29,341
Net income	$ 11,384	$ 10,081	$ 11,529	$ 11,778	$ 11,987	$ 11,765	$ 10,460	$ 10,034	44,772	44,246	43,548
Change in net unrealized gain during the period, tax									78	29	(162)
Change in net unrealized gain during the period, after tax									(98)	(36)	201
Total defined benefit plans, tax									(451)	2,685	(3,765)
Total other comprehensive income, before tax									(455)	(6,907)	8,896
Total other comprehensive income, tax									(201)	(3,119)	4,015
Total other comprehensive income (loss), net of tax									(254)	(3,788)	4,881
Securities Held-To-Maturity and Transferred Securities [Member]
Other Comprehensive Income (Loss) [Abstract]
Change in non-credit component of OTTI, pre-tax									(9)	32	32
Change in non-credit component of OTTI, tax									(4)	16	16
Change in non-credit component of OTTI, after tax									(5)	16	16
Change in unrealized loss on securities transferred to held to maturity, pre-tax									125	65	271
Change in unrealized loss on securities transferred to held to maturity, tax									54	29	122
Change in unrealized loss on securities transferred to held to maturity, after tax									71	36	149
Total Securities held to maturity and transferred securities, before tax									116	97	303
Total securities held to maturity and transferred, tax									50	45	138
Total securities held to maturity and transferred securities, after tax									66	52	165
Securities Available-For-Sale [Member]
Other Comprehensive Income (Loss) [Abstract]
Reclassification adjustment for net gains included in net gain on securities									(1,384)	(997)	(110)
Tax expense (benefit)									(624)	(450)	(50)
Net income									(760)	(547)	(60)
Change in net unrealized gain during the period, pre-tax									(176)	(65)	363
Change in net unrealized gain during the period, tax									(78)	(29)	162
Change in net unrealized gain during the period, after tax									(98)	(36)	201
Total securities available-for-sale, pre-tax									(1,560)	(1,062)	253
Total securities available-for-sale, tax									(702)	(479)	112
Total securities available-for-sale, after tax									(858)	(583)	141
Defined Benefit Plans [Member]
Other Comprehensive Income (Loss) [Abstract]
Reclassification adjustment for expense included in salaries and employee benefits expense									1,890	1,044	2,396
Tax expense (benefit)									852	468	1,082
Net income									1,038	576	1,314
Change in the net actuarial gain or loss, pre-tax									(901)	(6,986)	5,944
Change in the net actuarial gain or loss, tax									(401)	(3,153)	2,683
Change in the net actuarial gain or loss, after tax									(500)	(3,833)	3,261
Total defined benefit plans, pre-tax									989	(5,942)	8,340
Total defined benefit plans, tax									451	(2,685)	3,765
Total defined benefit plans, after tax									$ 538	$ (3,257)	$ 4,575