INVESTMENT SECURITIES - OTHER THAN TEMPORARY IMPAIRMENT (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Bank's private label mortgage backed security credit losses recognized in earnings
Number of securities held	176	173
Available-for-sale debt securities, at fair value (amortized cost of $531,974 in 2020 and $467,122 in 2019, allowance for credit losses of $126 in 2020 and $0 in 2019)	$ 543,859	$ 471,355
Private label mortgage backed security
Bank's private label mortgage backed security credit losses recognized in earnings
Number of securities held	1
Available-for-sale debt securities, at fair value (amortized cost of $531,974 in 2020 and $467,122 in 2019, allowance for credit losses of $126 in 2020 and $0 in 2019)	$ 3,249	$ 3,495