ACCUMULATED OTHER COMPREHENSIVE LOSS - Summary of Changes in Accumulated Other Comprehensive Income or Loss by Component (Details) - USD ($) $ in Thousands		3 Months Ended
		Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Changes in accumulated other comprehensive income or loss by component, net of tax [Roll Forward]
Beginning balances		$ 149,813	$ 143,748
Cumulative effect of accounting change	[1]			$ (162)
Balances at January 1, 2018, as adjusted				149,651
Total other comprehensive income (loss)		(3,294)	1,998
Ending balances		150,262	148,257
Accumulated Other Comprehensive Loss
Changes in accumulated other comprehensive income or loss by component, net of tax [Roll Forward]
Beginning balances		(10,340)	(10,754)
Cumulative effect of accounting change	[1]			(202)
Balances at January 1, 2018, as adjusted				(10,542)
Other comprehensive income before reclassification		(3,307)	1,977
Amounts reclassified from accumulated other comprehensive income		13	21
Total other comprehensive income (loss)		(3,294)	1,998
Ending balances		(13,836)	(8,756)
Unrealized Gains and Losses on Securities Available for Sale
Changes in accumulated other comprehensive income or loss by component, net of tax [Roll Forward]
Beginning balances		(3,415)	(4,356)
Cumulative effect of accounting change				(202)
Balances at January 1, 2018, as adjusted				(3,617)
Other comprehensive income before reclassification		(3,307)	1,977
Amounts reclassified from accumulated other comprehensive income		0	0
Total other comprehensive income (loss)		(3,307)	1,977
Ending balances		(6,924)	(2,379)
Defined Benefit and Other Benefit Plans
Changes in accumulated other comprehensive income or loss by component, net of tax [Roll Forward]
Beginning balances		(6,925)	(6,398)
Cumulative effect of accounting change				0
Balances at January 1, 2018, as adjusted				$ (6,925)
Other comprehensive income before reclassification		0	0
Amounts reclassified from accumulated other comprehensive income		13	21
Total other comprehensive income (loss)		13	21
Ending balances		$ (6,912)	$ (6,377)

[1] Due to implementation of ASC 2016-01. See "Adoption of New Accounting Standards" discussion in Note 1.