SECURITIES (Securities Debt Maturities) (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Investments, Debt and Equity Securities [Abstract]
Trading Securities, Amortized Cost, Maturing in one year or less	$ 0
Trading Securities, Amortized Cost, Maturing after one year through five years	0
Trading Securities, Amortized Cost, Maturing after five years through ten years	0
Trading Securities, Amortized Cost, Maturing after ten years through twenty years	27,203
Trading Securities, Amortized Cost, Maturing after twenty years	0
Debt Securities, Trading, Amortized Cost	27,203	$ 27,203
Trading Securities, Fair Value, Maturing in one year or less	0
Trading Securities, Fair Value, Maturing after one year through five years	0
Trading Securities, Fair Value, Maturing after five years through ten years	0
Trading Securities, Fair Value, Maturing after ten years through twenty years	26,875
Trading Securities, Fair Value, Maturing after twenty years	0
Trading Securities, Fair Value	26,875	24,980
Available-for-sale Securities, Amortized Cost, Maturing in one year or less	59,150
Available-for-sale Securities, Amortized Cost, Maturing after one year through five years	173,666
Available-for-sale Securities, Amortized Cost, Maturing after five years through ten years	845,638
Available-for-sale Securities, Amortized Cost, Maturing after ten years through twenty years	502,832
Available-for-sale Securities, Amortized Cost, Maturing after twenty years	1,862,230
Debt Securities, Available-for-sale, Amortized Cost, Total	3,443,516	2,256,189
Available-for-sale Securities, Fair Value, Maturing in one year or less	59,360
Available-for-sale Securities, Fair Value, Maturing after one year through five years	181,152
Available-for-sale Securities, Fair Value, Maturing after five years through ten years	847,708
Available-for-sale Securities, Fair Value, Maturing after ten years through twenty years	514,271
Available-for-sale Securities, Fair Value, Maturing after twenty years	1,844,084
Debt Securities, Available-for-sale	3,446,575	2,322,593
Held-to-maturity Securities, Amortized Cost, Maturing in one year or less	5,444
Held-to-maturity Securities, Amortized Cost, Maturing after one year through five years	59,705
Held-to-maturity Securities, Amortized Cost, Maturing after five years through ten years	21,961
Held-to-maturity Securities, Amortized Cost, Maturing after ten years through twenty years	164,303
Held-to-maturity Securities, Amortized Cost, Maturing after twenty years	196,399
Held-to-maturity Securities, Amortized Cost	447,812	421,807
Held-to-maturity Securities, Fair Value, Maturing in one year or less	5,471
Held-to-maturity Securities, Fair Value, Maturing after one year through five years	62,039
Held-to-maturity Securities, Fair Value, Maturing after five years through ten years	23,312
Held-to-maturity Securities, Fair Value, Maturing after ten years through twenty years	168,315
Held-to-maturity Securities, Fair Value, Maturing after twenty years	206,865
Debt Securities, Held-to-maturity, Fair Value	$ 466,002	$ 448,681