Summary of Significant Accounting Policies (Tables)

9 Months Ended

Sep. 30, 2022

Accounting Policies [Abstract]

Schedule of Goodwill and Intangible Assets

	September 30,		December 31,
(in thousands)	2022		2021
Goodwill
Surety	$	40,816	$	40,816
Casualty		5,246		5,246
Total goodwill	$	46,062	$	46,062
Intangibles
Indefinite-lived intangibles - state insurance licenses		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 September 30, 2022						Ended September 30, 2021
	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	$	439,893		45,379	$	9.69	$	29,243		45,243	$	0.65
Effect of Dilutive Securities
Stock options and restricted stock units		—		396				—		446
Diluted EPS
Earnings available to common shareholders	$	439,893		45,775	$	9.61	$	29,243		45,689	$	0.64
Anti-dilutive securities excluded from diluted EPS				435						191
	For the Nine Months						For the Nine Months
	Ended September 30, 2022						Ended September 30, 2021
	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	$	485,577		45,347	$	10.71	$	184,070		45,216	$	4.07
Effect of Dilutive Securities
Stock options and restricted stock units		—		428				—		498
Diluted EPS
Earnings available to common shareholders	$	485,577		45,775	$	10.61	$	184,070		45,714	$	4.03
Anti-dilutive securities excluded from diluted EPS				459						191

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

(in thousands)	For the Three Months				For the Nine Months
	Ended September 30,				Ended September 30,
Unrealized Gains/Losses on Available-for-Sale Securities	2022		2021		2022		2021
Beginning balance	$	(163,318)	$	79,144	$	49,826	$	108,714
Other comprehensive earnings (loss) before reclassifications		(82,785)		(12,114)		(296,422)		(40,307)
Amounts reclassified from accumulated other comprehensive earnings		1,537		(126)		2,030		(1,503)
Net current-period other comprehensive earnings (loss)	$	(81,248)	$	(12,240)	$	(294,392)	$	(41,810)
Ending balance	$	(244,566)	$	66,904	$	(244,566)	$	66,904
Balance of securities for which an allowance for credit losses has been recognized in net earnings					$	1,520	$	426

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 Nine Months
Component of Accumulated	Ended September 30,				Ended September 30,				Affected line item in the
Other Comprehensive Earnings (Loss)	2022		2021		2022		2021		Statement of Earnings
Unrealized gains and losses on available-for-sale securities	$	(1,912)	$	182	$	(2,684)	$	1,731	Net realized gains (losses)
		(34)		(22)		115		171	Credit gains presented within net realized gains
	$	(1,946)	$	160	$	(2,569)	$	1,902	Earnings (loss) before income taxes
		409		(34)		539		(399)	Income tax (expense) benefit
	$	(1,537)	$	126	$	(2,030)	$	1,503	Net earnings (loss)