
	2021				2020
	Amortized Cost		Estimated Fair Value		Amortized Cost		Estimated Fair Value
U.S. treasury notes and bonds	$	61,084	$	60,431	$	—	$	—
Mortgage-backed securities, residential	$	582,060	$	577,361	$	458,245	$	467,866

Obligations of states and political subdivisions	40,299		42,303		40,662		43,405
Corporate bonds and notes	22,750		22,848		9,000		9,035
SBA loan pools	89,216		89,083		34,455		34,305


Total	$	795,409	$	792,026	$	542,362	$	554,611

Gross unrealized gains and losses on securities available for sale at December 31, 2021 and 2020, were as follows (in thousands):


	2021				2020
	Unrealized Gains		Unrealized Losses		Unrealized Gains		Unrealized Losses
U.S. treasury notes and bonds	$	27	$	680	$	—	$	—
Mortgage-backed securities, residential	$	4,032	$	8,731	$	9,822	$	201

Obligations of states and political subdivisions	2,004		—		2,743		—
Corporate bonds and notes	180		82		47		12
SBA loan pools	344		477		42		192


Total	$	6,587	$	9,970	$	12,654	$	405

The amortized cost and estimated fair value of debt securities available for sale are shown below by contractual maturity. Expected maturities may differ from contractual maturities if borrowers have the right to call or prepay obligations with or without call or prepayment penalties. Securities not due at a single maturity date are shown separately (in thousands):


	December 31, 2021
	Amortized Cost		Fair Value
Within one year	$	1,302	$	1,307
After one, but within five years	37,598		39,099
After five, but within ten years	25,087		25,652
After ten years	470		500
Mortgage-backed securities, residential	582,060		577,361
U.S. treasury notes and bonds	59,676		59,024
SBA loan pools	89,216		89,083
Total	$	795,409	$	792,026

Actual maturities may differ from contractual maturities above because issuers may have the right to call or prepay obligations with or without call or prepayment penalties.

Amortized cost and estimated fair value of securities held to maturity at December 31, 2021 and 2020 are as follows (in thousands):


	2021				2020
	Amortized Cost		Estimated Fair Value		Amortized Cost		Estimated Fair Value
Obligations of states and political subdivisions	$	2,157	$	2,157	$	326	$	326
Time deposits with other financial institutions	1,633		1,639		2,143		2,175
	$	3,790	$	3,796	$	2,469	$	2,501

Gross unrealized gains and losses on securities held to maturity at December 31, 2021 and 2020, were as follows (in thousands):


	2021				2020
	Unrealized Gains		Unrealized Losses		Unrealized Gains		Unrealized Losses

Time deposits with other financial institutions	$	6	$	—	$	32	$	—
Total	$	6	$	—	$	32	$	—


	December 31, 2021
	Amortized Cost		Fair Value
Within one year	$	2,171	$	2,176
After one, but within five years	819		820
After five, but within ten years	800		800

Total	$	3,790	$	3,796

The following table summarizes the investment securities available for sale with unrealized losses at December 31, 2021 and December 31, 2020 by aggregated major security type and length of time in a continuous unrealized position (in thousands):


	Less than 12 months				12 months or longer				Total
	Fair Value		Unrealized Losses		Fair Value		Unrealized Losses		Fair Value		Unrealized Losses
2021
U.S. treasury notes and bonds	$	49,084	$	680	$	—	$	—	$	49,084	$	680
Mortgage-backed securities, residential	293,720		4,502		122,050		4,229		415,770		8,731

Corporate bonds and notes	4,928		72		1,989		10		6,917		82
SBA loan pools	51,235		296		13,769		181		65,004		477
Total temporarily impaired securities	$	398,967	$	5,550	$	137,808	$	4,420	$	536,775	$	9,970


	Less than 12 months				12 months or longer				Total
	Fair Value		Unrealized Losses		Fair Value		Unrealized Losses		Fair Value		Unrealized Losses
2020

Mortgage-backed securities, residential	$	70,037	$	200	$	970	$	1	$	71,007	$	201

Corporate bonds and notes	2,988		12		—		—		2,988		12
SBA loan pools	15,245		156		3,636		36		18,881		192
Total temporarily impaired securities	$	88,270	$	368	$	4,606	$	37	$	92,876	$	405

As of December 31, 2021, the majority of the Corporation’s unrealized losses in the investment securities portfolio related to mortgage-backed securities. At December 31, 2021, the unrealized losses related to mortgage-backed securities issued by U.S. government sponsored entities, Fannie Mae and Freddie Mac as well as corporate bonds and notes. Because the decline in fair value is attributable to changes in interest rates and not credit quality, and because the Corporation does not have the intent to sell these securities and it is not likely that it will be required to sell these securities before their anticipated recovery, the Corporation does not consider these securities to be other-than-temporarily impaired at December 31, 2021.

The fair value of securities pledged to secure public funds on deposit or for other purposes as required by law was $242.9 million at December 31, 2021 and $180.8 million at December 31, 2020.

There are no securities of a single issuer (other than securities of U.S. Government sponsored enterprises) that exceed 10% of shareholders' equity at December 31, 2021 or 2020.

The Corporation has an equity investment in Cephas Capital Partners, L.P. This small business investment company was established for the purpose of providing financing to small businesses in market areas served by the Corporation, including minority-owned small businesses and those that are anticipated to create jobs for the low to moderate income levels in the targeted areas. As of December 31, 2021 and 2020, this investment totaled $0.1 million and $0.2 million, respectively, is included in other assets, and is accounted for under the equity method of accounting.