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 September 30, 2021 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	$	469,445	$	(45	)	$	469,400	$	25,849	$	(158	)	$	495,091
Corporate bonds		51,974		(123	)		51,851		1,892		(4	)		53,739
U.S. agency-based mortgage-backed securities		5,060		—			5,060		474		—			5,534
U.S. Treasury securities and obligations of U.S. government agencies		14,801		—			14,801		167		(4	)		14,964
Asset-backed securities		116		(4	)		112		5		—			117
Totals	$	541,396	$	(172	)	$	541,224	$	28,387	$	(166	)	$	569,445

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 September 30, 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	$	209,354	$	15,010	$	(105	)	$	224,259	$	—
Corporate bonds		79,336		3,500		(99	)		82,737		—
U.S. agency-based mortgage-backed securities		9,487		237		(9	)		9,715		—
U.S. Treasury securities and obligations of U.S. government agencies		24,686		518		(77	)		25,127		—
Totals	$	322,863	$	19,265	$	(290	)	$	341,838	$	—

The cost, gross unrealized gains and losses, and the fair value of equity securities at September 30, 2021 are summarized as follows:

	Cost		Gross Unrealized Gains		Gross Unrealized Losses		Fair Value
	(in thousands)
Equity securities:
Domestic common stock	$	40,674	$	15,677	$	—	$	56,351
Total equity securities	$	40,674	$	15,677	$	—	$	56,351

	Amortized Cost		Allowance for Credit Losses			Carrying Amount		Gross Unrecognized Gains		Gross Unrecognized Losses		Fair Value
	(in thousands)
States and political subdivisions	$	494,374	$	(42	)	$	494,332	$	32,489	$	—	$	526,821
Corporate bonds		69,981		(225	)		69,756		3,144		—		72,900
U.S. agency-based mortgage-backed securities		7,261		—			7,261		645		—		7,906
U.S. Treasury securities and obligations of U.S. government agencies		13,626		—			13,626		239		—		13,865
Asset-backed securities		162		(7	)		155		7		—		162
Totals	$	585,404	$	(274	)	$	585,130	$	36,524	$	—	$	621,654

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, 2020 are summarized as follows:

	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Fair Value		Allowance for Credit Losses
	(in thousands)
States and political subdivisions	$	256,492	$	20,050	$	—		$	276,542	$	—
Corporate bonds		83,646		5,256		(3	)		88,899		—
U.S. agency-based mortgage-backed securities		18,654		400		(2	)		19,052		—
U.S. Treasury securities and obligations of U.S. government agencies		28,873		913		—			29,786		—
Totals	$	387,665	$	26,619	$	(5	)	$	414,279	$	—

The cost, gross unrealized gains and losses, and the fair value of equity securities at December 31, 2020 are summarized as follows:

	Cost		Gross Unrealized Gains		Gross Unrealized Losses		Fair Value
	(in thousands)
Equity securities:
Domestic common stock	$	35,787	$	7,650	$	—	$	43,437
Total equity securities	$	35,787	$	7,650	$	—	$	43,437

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:

	September 30, 2021				December 31, 2020
	Carrying Amount		Fair Value		Carrying Amount		Fair Value
	(in thousands)
Maturity:
Within one year	$	57,626	$	58,183	$	54,316	$	54,794
After one year through five years		169,880		176,260		195,706		204,289
After five years through ten years		105,046		110,513		107,347		113,643
After ten years		203,500		218,838		220,345		240,860
U.S. agency-based mortgage-backed securities		5,060		5,534		7,261		7,906
Asset-backed securities		112		117		155		162
Totals	$	541,224	$	569,445	$	585,130	$	621,654

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:

	September 30, 2021				December 31, 2020
	Amortized Cost		Fair Value		Amortized Cost		Fair Value
	(in thousands)
Maturity:
Within one year	$	32,152	$	32,718	$	69,177	$	69,938
After one year through five years		88,065		92,012		80,593		85,829
After five years through ten years		56,405		58,625		53,835		57,829
After ten years		136,754		148,768		165,406		181,631
U.S. agency-based mortgage-backed securities		9,487		9,715		18,654		19,052
Totals	$	322,863	$	341,838	$	387,665	$	414,279

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 September 30, 2021:

	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)
September 30, 2021
Available-for-Sale
States and political subdivisions	$	6,992	$	105	$	—	$	—	$	6,992	$	105
Corporate bonds		11,504		99		—		—		11,504		99
U.S. agency-based mortgage-backed securities		1,337		9		—		—		1,337		9
U.S. Treasury securities and obligations of U.S. government agencies		6,821		77		—		—		6,821		77
Total available-for-sale securities	$	26,654	$	290	$	—	$	—	$	26,654	$	290

At September 30, 2021, we held 22 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, 2020
Available-for-Sale
Corporate bonds	$	2,515	$	3	$	—	$	—	$	2,515	$	3
U.S. agency-based mortgage-backed securities		2,133		2		—		—		2,133		2
Total available-for-sale securities	$	4,648	$	5	$	—	$	—	$	4,648	$	5

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 quarter ended September 30, 2021.

	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 June 30, 2021	$	41	$	111	$	—	$	—	$	5		$	157
Provision for credit loss expense (benefit)		4		12		—		—		(1	)		15
Balance at September 30, 2021	$	45	$	123	$	—	$	—	$	4		$	172

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 nine months ended September 30, 2021.

	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, 2020	$	42	$	225		$	—	$	—	$	7		$	274
Provision for credit loss expense (benefit)		3		(102	)		—		—		(3	)		(102	)
Balance at September 30, 2021	$	45	$	123		$	—	$	—	$	4		$	172

The Company has established an allowance for credit losses on 378 held-to-maturity securities totaling $0.2 million. The majority of those securities were issued by states and political subdivisions (355 securities) and corporate bonds (20 securities).

The Company has no allowance for credit losses on investments classified as available-for-sale for the period ended September 30, 2021.

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 September 30, 2021.

	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	$	466,450	$	22,647	$	5,060	$	14,801	$	79	$	509,037
Baa/BBB ratings		2,995		29,327		—		—		16		32,338
B ratings		—		—		—		—		21		21
Total	$	469,445	$	51,974	$	5,060	$	14,801	$	116	$	541,396

Net realized losses in the quarter ended September 30, 2021 were immaterial. Net realized gains in the quarter ended September 30, 2020 were $0.3 million resulting from the call of fixed maturity securities.

Net realized gains in the nine months ended September 30, 2021 were $1.5 million resulting primarily from the sale of fixed maturity securities classified as available-for-sale. Net realized gains in the nine months ended September 30, 2020 were $1.5 million resulting primarily from the sale of fixed maturity securities classified as available-for-sale and from called fixed maturity securities.

During the third quarter of 2021, we recognized through income $0.8 million of net unrealized losses on equity securities held as of September 30, 2021. During the third quarter of 2020, we recognized through income $0.8 million of net unrealized gains on equity securities held as of September 30, 2020.

During the nine months ended September 30, 2021, we recognized through income $8.0 million of net unrealized gains on equity securities held as of September 30, 2021. During the nine months ended September 30, 2020, we recognized through income $2.3 million of net unrealized losses on equity securities held as of September 30, 2020.

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.