Basis of Presentation and Summary of Significant Accounting Policies (Tables)

3 Months Ended

Mar. 31, 2026

Accounting Policies [Abstract]

Schedule of Goodwill and Intangible Assets

	March 31,		December 31,
(in thousands)	2026		2025
Goodwill
Surety	$	40,816	$	40,816
Casualty		5,246		5,246
Total goodwill	$	46,062	$	46,062
Indefinite-lived intangibles		7,500		7,500
Total goodwill and intangibles	$	53,562	$	53,562

Schedule of Reconciliation of Numerator and Denominator of the Basic and Diluted Earnings Per Share Computations

	For the Three Months						For the Three Months
	Ended March 31, 2026						Ended March 31, 2025
	Income		Shares		Per Share		Income		Shares		Per Share
(in thousands, except per share data)	(Numerator)		(Denominator)		Amount		(Numerator)		(Denominator)		Amount
Basic EPS
Earnings available to common shareholders	$	54,885		91,926	$	0.60	$	63,214		91,770	$	0.69
Effect of Dilutive Securities
Stock options and restricted stock units		—		261				—		758
Diluted EPS
Earnings available to common shareholders	$	54,885		92,187	$	0.60	$	63,214		92,528	$	0.68
Anti-dilutive securities excluded from diluted EPS				1,066						48

Schedule of Changes in the Balance of Each Component of Accumulated Other Comprehensive Earnings (Loss)

(in thousands)	For the Three Months
	Ended March 31,
Unrealized Gains (Losses) on Available-for-Sale Securities	2026		2025
Beginning balance	$	(88,074)	$	(173,723)
Other comprehensive earnings (loss) before reclassifications		(25,977)		29,899
Amounts reclassified from accumulated other comprehensive earnings		611		131
Net current-period other comprehensive earnings (loss)	$	(25,366)	$	30,030
Ending balance	$	(113,440)	$	(143,693)
Balance of securities for which an allowance for credit losses has been recognized in net earnings		1,710		1,692

Schedule of Effects of Reclassifications out of Accumulated Other Comprehensive Earnings (Loss)

	Amount Reclassified from Accumulated Other
(in thousands)	Comprehensive Earnings (Loss)
	For the Three Months
Component of Accumulated	Ended March 31,				Affected line item in the
Other Comprehensive Earnings (Loss)	2026		2025		Statement of Earnings
Unrealized gains and losses on available-for-sale securities	$	(1,063)	$	(205)	Net realized gains (losses)
		290		40	Credit gains (losses) presented within net realized gains
	$	(773)	$	(165)	Earnings (loss) before income taxes
		162		34	Income tax (expense) benefit
	$	(611)	$	(131)	Net earnings (loss)