REGULATORY CAPITAL - Narrative (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
Banking and Thrift, Other Disclosure [Abstract]
Busey bank paid dividends to the company, amount received	$ 160.0	$ 100.0	$ 90.0

Dividends received on equity and other investments during the current period.

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 230
-SubTopic 10
-Name Accounting Standards Codification
-Section 45
-Paragraph 16
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482740/230-10-45-16

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration