GOODWILL, OTHER INTANGIBLE ASSETS AND MORTGAGE SERVICING RIGHTS (Finite-Lived Intangible Assets) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Goodwill [Line Items]
Goodwill, beginning of period	$ 373,121	$ 373,121	$ 339,154
Intangible Assets, Net (Including Goodwill), beginning of period	394,547	402,279	372,078
Goodwill, Acquired During Period			33,967
Acquired Intangible Assets (Including Goodwill)			38,577
Amortization	(6,571)	(7,732)	(8,151)
Finite-Lived Intangible Assets, Other Changes			0
Intangible Assets (including Goodwill), Other Changes			(225)
Goodwill, end of period	373,121	373,121	373,121
Balance, end of period	14,855
Intangible Assets, Net (Including Goodwill), end of period	387,976	394,547	402,279
Core Deposit Intangibles [Member]
Goodwill [Line Items]
Balance, beginning of period	21,426	29,158	32,699
Additions through acquisition			4,610
Amortization	(6,571)	(7,732)	(8,151)
Balance, end of period	14,855	21,426	29,158
Other Intangible Assets [Member]
Goodwill [Line Items]
Balance, beginning of period	0	0	225
Additions through acquisition			0
Amortization	0	0	0
Balance, end of period	$ 0	$ 0	0
Other Intangible Assets [Member] | Accounting Standards Update 2016-02 Cumulative Effect, Period of Adoption
Goodwill [Line Items]
Finite-Lived Intangible Assets, Other Changes			$ (225)