The amortized cost, allowance for credit losses, carrying amount, gross unrecognized gains and losses, and the fair value of those investments classified as held-to-maturity at March 31, 2022 are summarized as follows:

	Amortized Cost		Allowance for Credit Losses			Carrying Amount		Gross Unrecognized Gains		Gross Unrecognized Losses			Fair Value
	(in thousands)
States and political subdivisions	$	458,118	$	(45	)	$	458,073	$	7,160	$	(5,936	)	$	459,297
Corporate bonds		66,944		(241	)		66,703		137		(1,371	)		65,469
U.S. agency-based mortgage-backed securities		4,285		—			4,285		167		(5	)		4,447
U.S. Treasury securities and obligations of U.S. government agencies		16,215		—			16,215		56		(159	)		16,112
Asset-backed securities		100		(4	)		96		4		—			100
Totals	$	545,662	$	(290	)	$	545,372	$	7,524	$	(7,471	)	$	545,425

The amortized cost, gross unrealized gains and losses, fair value, and the allowance for credit losses of those investments classified as available-for-sale at March 31, 2022 are summarized as follows:

	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Fair Value		Allowance for Credit Losses
	(in thousands)
States and political subdivisions	$	200,313	$	4,541	$	(2,618	)	$	202,236	$	—
Corporate bonds		114,642		780		(1,723	)		113,699		—
U.S. agency-based mortgage-backed securities		7,117		—		(155	)		6,962		—
U.S. Treasury securities and obligations of U.S. government agencies		20,712		17		(654	)		20,075		—
Totals	$	342,784	$	5,338	$	(5,150	)	$	342,972	$	—

The cost, gross unrealized gains and losses, and the fair value of equity securities at March 31, 2022 are summarized as follows:

	Cost		Gross Unrealized Gains		Gross Unrealized Losses		Fair Value
	(in thousands)
Equity securities:
Domestic common stock	$	48,151	$	21,005	$	—	$	69,156
Total equity securities	$	48,151	$	21,005	$	—	$	69,156

	Amortized Cost		Allowance for Credit Losses			Carrying Amount		Gross Unrecognized Gains		Gross Unrecognized Losses			Fair Value
	(in thousands)
States and political subdivisions	$	471,688	$	(48	)	$	471,640	$	25,175	$	(263	)	$	496,552
Corporate bonds		56,756		(143	)		56,613		1,344		(114	)		57,843
U.S. agency-based mortgage-backed securities		4,623		—			4,623		377		—			5,000
U.S. Treasury securities and obligations of U.S. government agencies		16,251		—			16,251		132		(36	)		16,347
Asset-backed securities		108		(4	)		104		4		—			108
Totals	$	549,426	$	(195	)	$	549,231	$	27,032	$	(413	)	$	575,850

The amortized cost, gross unrealized gains and losses, fair value, and the allowance for credit losses of those investments classified as available-for-sale at December 31, 2021 are summarized as follows:

	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Fair Value		Allowance for Credit Losses
	(in thousands)
States and political subdivisions	$	202,008	$	14,538	$	(240	)	$	216,306	$	—
Corporate bonds		93,947		2,751		(272	)		96,426		—
U.S. agency-based mortgage-backed securities		7,944		158		(13	)		8,089		—
U.S. Treasury securities and obligations of U.S. government agencies		20,698		382		(132	)		20,948		—
Totals	$	324,597	$	17,829	$	(657	)	$	341,769	$	—

The cost, gross unrealized gains and losses, and the fair value of equity securities at December 31, 2021 are summarized as follows:

	Cost		Gross Unrealized Gains		Gross Unrealized Losses		Fair Value
	(in thousands)
Equity securities:
Domestic common stock	$	44,175	$	19,965	$	—	$	64,140
Total equity securities	$	44,175	$	19,965	$	—	$	64,140

A summary of the carrying amounts and fair value of investments in fixed maturity securities classified as held-to-maturity, by contractual maturity, is as follows:

	March 31, 2022				December 31, 2021
	Carrying Amount		Fair Value		Carrying Amount		Fair Value
	(in thousands)
Maturity:
Within one year	$	68,986	$	69,161	$	70,859	$	71,455
After one year through five years		177,434		176,902		174,157		180,376
After five years through ten years		101,095		99,706		100,543		104,851
After ten years		193,476		195,109		198,945		214,060
U.S. agency-based mortgage-backed securities		4,285		4,447		4,623		5,000
Asset-backed securities		96		100		104		108
Totals	$	545,372	$	545,425	$	549,231	$	575,850

A summary of the amortized cost and fair value of investments in fixed maturity securities classified as available-for-sale, by contractual maturity, is as follows:

	March 31, 2022				December 31, 2021
	Amortized Cost		Fair Value		Amortized Cost		Fair Value
	(in thousands)
Maturity:
Within one year	$	30,304	$	30,282	$	30,925	$	31,258
After one year through five years		104,200		103,483		97,830		100,716
After five years through ten years		70,744		69,143		58,050		60,137
After ten years		130,419		133,102		129,848		141,569
U.S. agency-based mortgage-backed securities		7,117		6,962		7,944		8,089
Totals	$	342,784	$	342,972	$	324,597	$	341,769

The following table summarizes the fair value and gross unrealized losses on securities classified as available-for-sale, aggregated by major investment category and length of time that the individual securities have been in a continuous unrealized loss position as of March 31, 2022:

	Less Than 12 Months				12 Months or Greater				Total
	Fair Value of Investments with Unrealized Losses		Gross Unrealized Losses		Fair Value of Investments with Unrealized Losses		Gross Unrealized Losses		Fair Value of Investments with Unrealized Losses		Gross Unrealized Losses
	(in thousands)
March 31, 2022
Available-for-Sale
States and political subdivisions	$	62,574	$	2,618	$	—	$	—	$	62,574	$	2,618
Corporate bonds		66,857		1,723		—		—		66,857		1,723
U.S. agency-based mortgage-backed securities		6,962		155		—		—		6,962		155
U.S. Treasury securities and obligations of U.S. government agencies		14,067		654		—		—		14,067		654
Total available-for-sale securities	$	150,460	$	5,150	$	—	$	—	$	150,460	$	5,150

At March 31, 2022, we held 107 individual fixed maturity securities classified as available-for-sale that were in an unrealized loss position, of which none were in a continuous unrealized loss position for longer than 12 months.

	Less Than 12 Months				12 Months or Greater				Total
	Fair Value of Investments with Unrealized Losses		Gross Unrealized Losses		Fair Value of Investments with Unrealized Losses		Gross Unrealized Losses		Fair Value of Investments with Unrealized Losses		Gross Unrealized Losses
	(in thousands)
December 31, 2021
Available-for-Sale
States and political subdivisions	$	23,465	$	240	$	—	$	—	$	23,465	$	240
Corporate bonds		36,443		272		—		—		36,443		272
U.S. agency-based mortgage-backed securities		1,146		13		—		—		1,146		13
U.S. Treasury securities and obligations of U.S. government agencies		6,771		132		—		—		6,771		132
Total available-for-sale securities	$	67,825	$	657	$	—	$	—	$	67,825	$	657

The following table illustrates the changes in the allowance for credit losses by major security type of the investments classified as held-to-maturity for the three months ended March 31, 2022.

	States and Political Subdivisions			Corporate Bonds		U.S. Agency-Based Mortgage-Backed Securities		U.S. Treasury Securities and Obligations of U.S. Government Agencies		Asset-Backed Securities		Totals
	(in thousands)
Balance at December 31, 2021	$	48		$	143	$	—	$	—	$	4	$	195
Provision for credit loss expense (benefit)		(3	)		98		—		—		—		95
Balance at March 31, 2022	$	45		$	241	$	—	$	—	$	4	$	290

The Company has established an allowance for credit losses on 362 held-to-maturity securities totaling $0.3 million. The majority of those securities were issued by states and political subdivisions (333 securities) and corporate bonds (26 securities).

The Company has no allowance for credit losses on investments classified as available-for-sale for the period ended March 31, 2022.

The credit rating used for held-to-maturity fixed income securities is the rating for each security as published by Moody’s, S&P, and Fitch to determine the probability of default. If there are two ratings, the lower rating is used. If there are three ratings, the median rating is used. If there is one rating, that rating is used. For corporate fixed income securities (given a rating), the probability of default comes from Moody’s annual study of corporate bond defaults published each February. The maximum maturity using the default rate is 20 years (any maturity greater than 20 years will use the 20-year rate). For municipal fixed income securities (given a rating), the probability of default comes from Moody’s annual study of municipal bond defaults published each July/August.

The calculation of the credit loss allowance takes the amortized cost of the fixed income security and assumes default and recovery based on the average recovery rates from the Moody’s default studies. The amortized cost of the security, minus the amount recovered, is the estimated full amount the Company could lose in a default scenario. Then this amount is multiplied by the probability of default to determine the allowance for credit loss. The lower the security is rated, the higher likelihood of default, and therefore a higher allowance for credit loss. The longer to the maturity date of a security, the higher the default risk.

The table below presents the amortized cost of held-to-maturity securities aggregated by credit quality indicator as of March 31, 2022.

	States and Political Subdivisions		Corporate Bonds		U.S. Agency-Based Mortgage-Backed Securities		U.S. Treasury Securities and Obligations of U.S. Government Agencies		Asset-Backed Securities		Totals
	Amortized cost
	(in thousands)
AAA/AA/A ratings	$	455,133	$	27,507	$	4,285	$	16,215	$	70	$	503,210
Baa/BBB ratings		2,985		39,437		—		—		13		42,435
B ratings		—		—		—		—		17		17
Total	$	458,118	$	66,944	$	4,285	$	16,215	$	100	$	545,662

Net realized gains in the three months ended March 31, 2022 were $0.7 million resulting primarily from the sale of equity and fixed maturity securities classified as available-for-sale. Net realized gains in the three months ended March 31, 2021 were $0.3 million resulting primarily from the sale of fixed maturity securities classified as available-for-sale.

During the three months ended March 31, 2022, we recognized through income $1.0 million of net unrealized gains on equity securities held as of March 31, 2022. During the three months ended March 31, 2021, we recognized through income $5.5 million of net unrealized gains on equity securities held as of March 31, 2021.

Investment income is recognized as it is earned. The discount or premium on fixed maturity securities is amortized using the “constant yield” method. Anticipated prepayments, where applicable, are considered when determining the amortization of premiums or discounts. Realized investment gains and losses are determined using the specific identification method.