Investments, Unrealized Gain (Losses) on Investments (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
Debt Securities, Available-for-sale [Line Items]
Change in unrealized gains (losses), fixed-maturity securities	$ 84.2	$ (3.3)	$ 51.0

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

Kinsale Capital Group, Inc. 10-K