ACCUMULATED OTHER COMPREHENSIVE INCOME (LOSS), Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands		3 Months Ended		12 Months Ended
		Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance		$ 598,567	$ 565,868	$ 565,868
Other comprehensive income (loss) before reclassifications		499	207
Amounts reclassified from accumulated other comprehensive loss		(744)	218
Other comprehensive income (loss), net of tax		(275)	425
Reclassification of tax effects on other comprehensive income	[1]	32
Balance		$ 607,957	$ 573,225	$ 598,567
Corporate income tax rate		21.00%	35.00%	35.00%
ASU 2016-01 [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance		$ 598,567
Reclassification of unrealized gains and losses on available-for-sale equity securities				$ 0
Balance				598,567
Accumulated Other Comprehensive Gain (Loss) [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance		(3,641)	$ (5,939)	(5,939)
Balance		(4,037)	(5,514)	(3,641)
Accumulated Other Comprehensive Gain (Loss) [Member] | ASU 2016-01 [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance		(3,794)
Reclassification of unrealized gains and losses on available-for-sale equity securities	[2]			(153)
Balance				(3,794)
Securities Held-to-Maturity and Transferred Securities [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance		0	(713)	(713)
Other comprehensive income (loss) before reclassifications		0	18
Amounts reclassified from accumulated other comprehensive loss		0	0
Other comprehensive income (loss), net of tax		0	18
Reclassification of tax effects on other comprehensive income	[1]	0
Balance		0	(695)	0
Securities Held-to-Maturity and Transferred Securities [Member] | ASU 2016-01 [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance		0
Reclassification of unrealized gains and losses on available-for-sale equity securities	[2]			0
Balance				0
Securities Available-for-Sale [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance		285	(92)	(92)
Other comprehensive income (loss) before reclassifications		(786)	65
Amounts reclassified from accumulated other comprehensive loss		(922)	0
Other comprehensive income (loss), net of tax		(1,708)	65
Reclassification of tax effects on other comprehensive income	[1]	0
Balance		(1,576)	(27)	285
Securities Available-for-Sale [Member] | ASU 2016-01 [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance		132
Reclassification of unrealized gains and losses on available-for-sale equity securities	[2]			(153)
Balance				132
Defined Benefit Plans [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance		(6,633)	(6,910)	(6,910)
Other comprehensive income (loss) before reclassifications		(88)	0
Amounts reclassified from accumulated other comprehensive loss		192	171
Other comprehensive income (loss), net of tax		104	171
Reclassification of tax effects on other comprehensive income	[1]	32
Balance		(6,497)	(6,739)	(6,633)
Defined Benefit Plans [Member] | ASU 2016-01 [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance		(6,633)
Reclassification of unrealized gains and losses on available-for-sale equity securities	[2]			0
Balance				(6,633)
Derivative Asset [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance		2,707	1,776	1,776
Other comprehensive income (loss) before reclassifications		1,373	124
Amounts reclassified from accumulated other comprehensive loss		(44)	47
Other comprehensive income (loss), net of tax		1,329	171
Reclassification of tax effects on other comprehensive income	[1]	0
Balance		4,036	$ 1,947	2,707
Derivative Asset [Member] | ASU 2016-01 [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance		$ 2,707
Reclassification of unrealized gains and losses on available-for-sale equity securities	[2]			0
Balance				$ 2,707

[1] Represents the impact of adopting ASU 2018-02 allowing the reclassification of certain stranded income tax effects in accumulated other comprehensive income resulting from the Tax Cuts and Jobs Act of 2017 from accumulated other comprehensive income to retained earnings in each period in which the effect of the change in the U.S. federal corporate income tax rate in the Tax Cuts and Jobs Act of 2017 (the "Tax Act") (or portion thereof) is recorded. The amount of the reclassification is an adjustment for the difference between the historical corporate income tax rate (35%) and the newly enacted 21% corporate income tax rate.

[2] Represents the impact of adopting ASU 2016-01 allowing the reclassification of unrealized gains and losses on available-for-sale equity securities from accumulated other comprehensive income to retained earnings.