Investment Securities - Narrative (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023
Debt Securities, Available-for-sale [Line Items]
Investment in subsidiary bank	$ 944,136	$ 779,421
Amortized Cost	979,855	$ 814,839
Lower-yielding AFS debt securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	135,050
Pre-tax realized loss	5,220
Collateralized Securities
Debt Securities, Available-for-sale [Line Items]
Investment in subsidiary bank	$ 250,650

Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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+ Details

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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+ Details

HILLS BANCORPORATION 10-K