SECURITIES AVAILABLE FOR SALE - Gross unrealized losses and the related fair value of securities available for sale (Details) - Accounting Standards Update 2016-01 $ in Thousands	Dec. 31, 2018 USD ($) Security	Dec. 31, 2017 USD ($) Security
Debt Securities, Available-for-sale [Line Items]
Less than 12 months, Fair Value	$ 88,296	$ 218,748
Less than 12 months, Unrealized Losses	907	2,248
12 months or more, Fair Value	251,570	114,863
12 months or more, Unrealized Losses	7,290	2,765
Total, Fair Value	339,866	333,611
Total, Unrealized Losses	$ 8,197	$ 5,013
Number of Securities | Security	680	687
U.S. government agency securities
Debt Securities, Available-for-sale [Line Items]
Less than 12 months, Fair Value	$ 0	$ 26,209
Less than 12 months, Unrealized Losses	0	377
12 months or more, Fair Value	21,649	0
12 months or more, Unrealized Losses	818	0
Total, Fair Value	21,649	26,209
Total, Unrealized Losses	$ 818	$ 377
Number of Securities | Security	3	2
US States and Political Subdivisions Debt Securities
Debt Securities, Available-for-sale [Line Items]
Less than 12 months, Fair Value	$ 16,136	$ 110,157
Less than 12 months, Unrealized Losses	98	1,097
12 months or more, Fair Value	130,975	49,326
12 months or more, Unrealized Losses	3,154	1,167
Total, Fair Value	147,111	159,483
Total, Unrealized Losses	$ 3,252	$ 2,264
Number of Securities | Security	440	465
Mortgage-backed securities
Debt Securities, Available-for-sale [Line Items]
Less than 12 months, Fair Value	$ 20,568	$ 72,210
Less than 12 months, Unrealized Losses	132	735
12 months or more, Fair Value	89,189	65,537
12 months or more, Unrealized Losses	2,902	1,598
Total, Fair Value	109,757	137,747
Total, Unrealized Losses	$ 3,034	$ 2,333
Number of Securities | Security	204	215
Corporate debt securities
Debt Securities, Available-for-sale [Line Items]
Less than 12 months, Fair Value	$ 51,592	$ 10,172
Less than 12 months, Unrealized Losses	677	39
12 months or more, Fair Value	9,757	0
12 months or more, Unrealized Losses	416	0
Total, Fair Value	61,349	10,172
Total, Unrealized Losses	$ 1,093	$ 39
Number of Securities | Security	33	5