INVESTMENT SECURITIES - Investments in Any One Issuer Exceeding Ten Percent of Equity (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019
Concentration Risk [Line Items]
Investment securities available-for-sale at amortized cost	$ 1,198,513	$ 966,900
Available-for-sale, fair value	1,243,693	$ 978,284
Credit Concentration Risk
Concentration Risk [Line Items]
Investment securities available-for-sale at amortized cost	825,926
Available-for-sale, fair value	848,058
Credit Concentration Risk \| Federal Home Loan Mortgage Corporation
Concentration Risk [Line Items]
Investment securities available-for-sale at amortized cost	405,243
Available-for-sale, fair value	419,653
Credit Concentration Risk \| Federal Home Loan Bank
Concentration Risk [Line Items]
Investment securities available-for-sale at amortized cost	88,802
Available-for-sale, fair value	91,761
Credit Concentration Risk \| Federal National Mortgage Association
Concentration Risk [Line Items]
Investment securities available-for-sale at amortized cost	331,881
Available-for-sale, fair value	$ 336,644
Stockholders' Equity, Total
Concentration Risk [Line Items]
Concentration risk percentage	10.00%

Amortized cost of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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