Summary of Significant Accounting Policies (Tables)

6 Months Ended

Jun. 30, 2023

Accounting Policies [Abstract]

Schedule of Goodwill and Intangible Assets

	June 30,		December 31,
(in thousands)	2023		2022
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 June 30, 2023						Ended June 30, 2022
	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	$	77,652		45,591	$	1.70	$	(2,239)		45,354	$	(0.05)
Effect of Dilutive Securities
Stock options and restricted stock units		—		453				—		—
Diluted EPS
Earnings available to common shareholders	$	77,652		46,044	$	1.69	$	(2,239)		45,354	$	(0.05)
Anti-dilutive securities excluded from diluted EPS				118						736
	For the Six Months						For the Six Months
	Ended June 30, 2023						Ended June 30, 2022
	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	$	176,463		45,560	$	3.87	$	45,684		45,330	$	1.01
Effect of Dilutive Securities
Stock options and restricted stock units		—		485				—		418
Diluted EPS
Earnings available to common shareholders	$	176,463		46,045	$	3.83	$	45,684		45,748	$	1.00
Anti-dilutive securities excluded from diluted EPS				118						436

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

(in thousands)	For the Three Months				For the Six Months
	Ended June 30,				Ended June 30,
Unrealized Gains/Losses on Available-for-Sale Securities	2023		2022		2023		2022
Beginning balance	$	(191,369)	$	(65,755)	$	(229,076)	$	49,826
Other comprehensive earnings (loss) before reclassifications		(20,347)		(97,894)		15,908		(213,636)
Amounts reclassified from accumulated other comprehensive earnings		626		331		2,078		492
Net current-period other comprehensive earnings (loss)	$	(19,721)	$	(97,563)	$	17,986	$	(213,144)
Ending balance	$	(211,090)	$	(163,318)	$	(211,090)	$	(163,318)
Balance of securities for which an allowance for credit losses has been recognized in net earnings					$	1,053	$	1,083

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				For the Six Months
Component of Accumulated	Ended June 30,				Ended June 30,				Affected line item in the
Other Comprehensive Earnings (Loss)	2023		2022		2023		2022		Statement of Earnings
Unrealized gains and losses on available-for-sale securities	$	(824)	$	(722)	$	(2,536)	$	(772)	Net realized gains (losses)
		31		303		(95)		149	Credit gains presented within net realized gains
	$	(793)	$	(419)	$	(2,631)	$	(623)	Earnings (loss) before income taxes
		167		88		553		131	Income tax (expense) benefit
	$	(626)	$	(331)	$	(2,078)	$	(492)	Net earnings (loss)