INVESTMENT SECURITIES - Schedule of Debt Securities (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Investment securities available-for-sale:
Amortized Cost	$ 1,198,513	$ 966,900
Unrealized Gains	45,805	15,002
Unrealized Losses	(625)	(3,618)
Available-for-sale, fair value	1,243,693	978,284
Investment securities held-to-maturity:
Amortized Cost	35,223	48,212
Unrealized Gains	719	53
Unrealized Losses	0	(316)
Fair Value	35,942	47,949
Equity Securities, FV-NI [Abstract]
Amortized cost	41,452	18,810
Fair Value	41,452	18,810
U.S. government and agencies
Investment securities available-for-sale:
Amortized Cost	19,962	19,955
Unrealized Gains	1,022	42
Unrealized Losses	0	(57)
Available-for-sale, fair value	20,984	19,940
Government-sponsored entities
Investment securities available-for-sale:
Amortized Cost	142,985	154,963
Unrealized Gains	4,801	1,292
Unrealized Losses	0	0
Available-for-sale, fair value	147,786	156,255
Municipal bonds
Investment securities available-for-sale:
Amortized Cost	324,422	312,977
Unrealized Gains	22,177	12,551
Unrealized Losses	(11)	(73)
Available-for-sale, fair value	346,588	325,455
Mortgage-backed securities
Investment securities available-for-sale:
Amortized Cost	711,144	479,005
Unrealized Gains	17,805	1,117
Unrealized Losses	(614)	(3,488)
Available-for-sale, fair value	728,335	476,634
Investment securities held-to-maturity:
Amortized Cost	35,223	48,212
Unrealized Gains	719	53
Unrealized Losses	0	(316)
Fair Value	35,942	47,949
Money market mutual funds
Equity Securities, FV-NI [Abstract]
Amortized cost	41,452	18,810
Fair Value	$ 41,452	$ 18,810

Equity Securities, FV-NI [Abstract]

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