INVESTMENT SECURITIES - Maturities of Available for sale Securities by Type (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Debt Securities, Available-for-sale, Amortized Cost, Fiscal Year Maturity [Abstract]
Amortized Cost	$ 1,198,513	$ 966,900
Debt Securities, Available-for-sale, Fair Value, Fiscal Year Maturity [Abstract]
Total	1,243,693	978,284
U.S. government and agencies
Debt Securities, Available-for-sale, Amortized Cost, Fiscal Year Maturity [Abstract]
Within one year	0
After one, but within five years	10,000
After five, but within ten years	9,962
Greater than ten years	0
Amortized Cost	19,962	19,955
Debt Securities, Available-for-sale, Fair Value, Fiscal Year Maturity [Abstract]
Within one year	0
After one, but within five years	10,337
After five, but within ten years	10,647
Greater than ten years	0
Total	$ 20,984	19,940
Debt Securities, Available-for-sale, Maturity, Weighted Average Yield [Abstract]
Within one year	0.00%
After one, but within five years	1.75%
After five, but within ten years	1.70%
Greater than ten years	0.00%
Total	1.72%
Government-sponsored entities
Debt Securities, Available-for-sale, Amortized Cost, Fiscal Year Maturity [Abstract]
Within one year	$ 27,776
After one, but within five years	100,116
After five, but within ten years	15,093
Greater than ten years	0
Amortized Cost	142,985	154,963
Debt Securities, Available-for-sale, Fair Value, Fiscal Year Maturity [Abstract]
Within one year	28,107
After one, but within five years	103,336
After five, but within ten years	16,343
Greater than ten years	0
Total	$ 147,786	156,255
Debt Securities, Available-for-sale, Maturity, Weighted Average Yield [Abstract]
Within one year	1.89%
After one, but within five years	1.99%
After five, but within ten years	2.00%
Greater than ten years	0.00%
Total	1.97%
Municipal bonds
Debt Securities, Available-for-sale, Amortized Cost, Fiscal Year Maturity [Abstract]
Within one year	$ 10,582
After one, but within five years	10,678
After five, but within ten years	87,513
Greater than ten years	215,649
Amortized Cost	324,422	312,977
Debt Securities, Available-for-sale, Fair Value, Fiscal Year Maturity [Abstract]
Within one year	10,676
After one, but within five years	10,895
After five, but within ten years	93,603
Greater than ten years	231,414
Total	$ 346,588	325,455
Debt Securities, Available-for-sale, Maturity, Weighted Average Yield [Abstract]
Within one year	2.16%
After one, but within five years	2.39%
After five, but within ten years	2.60%
Greater than ten years	2.43%
Total	2.47%
Mortgage-backed securities
Debt Securities, Available-for-sale, Amortized Cost, Fiscal Year Maturity [Abstract]
Within one year	$ 9,310
After one, but within five years	170,295
After five, but within ten years	121,639
Greater than ten years	409,900
Amortized Cost	711,144	479,005
Debt Securities, Available-for-sale, Fair Value, Fiscal Year Maturity [Abstract]
Within one year	9,341
After one, but within five years	179,035
After five, but within ten years	127,337
Greater than ten years	412,622
Total	$ 728,335	$ 476,634
Debt Securities, Available-for-sale, Maturity, Weighted Average Yield [Abstract]
Within one year	2.22%
After one, but within five years	2.16%
After five, but within ten years	2.12%
Greater than ten years	1.44%
Total	1.74%