The amortized cost, gross unrealized gains and losses and estimated fair value of securities at December 31, 2021 and December 31, 2020 are summarized as follows (in thousands):


	December 31, 2021
	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses		Allowance for Credit Losses		Fair Value
Available-for-Sale:
U.S. Government and agency obligations	$	201,101	$	852	$	(621)	$	—	$	201,332
Municipal bonds	293,761		15,171		(320)		—		308,612
Corporate bonds	114,427		3,103		(183)		—		117,347
Mortgage-backed or related securities	2,837,480		17,749		(49,961)		—		2,805,268
Asset-backed securities	206,391		52		(9)		—		206,434

	$	3,653,160	$	36,927	$	(51,094)	$	—	$	3,638,993


	December 31, 2021
	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses		Fair Value		Allowance for Credit Losses
Held-to-Maturity:
U.S. Government and agency obligations	$	316	$	3	$	—	$	319	$	—
Municipal bonds	420,555		20,743		(1,393)		439,905		(203)
Corporate bonds	3,092		—		(3)		3,089		(230)
Mortgage-backed or related securities	97,392		1,171		(23)		98,540		—
	$	521,355	$	21,917	$	(1,419)	$	541,853	$	(433)


	December 31, 2020
	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses		Allowance for Credit Losses		Fair Value
Available-for-Sale:
U.S. Government and agency obligations	$	141,668	$	1,002	$	(935)	$	—	$	141,735
Municipal bonds	283,997		19,523		(2)		—		303,518
Corporate bonds	219,086		2,762		(79)		—		221,769
Mortgage-backed or related securities	1,602,033		45,179		(1,060)		—		1,646,152
Asset-backed securities	9,405		77		(63)		—		9,419

	$	2,256,189	$	68,543	$	(2,139)	$	—	$	2,322,593


	December 31, 2020
	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses		Fair Value		Allowance for Credit Losses
Held-to-Maturity:
U.S. Government and agency obligations	$	340	$	7	$	—	$	347	$	—
Municipal bonds	370,998		24,130		(94)		395,034		(59)
Corporate bonds	3,222		—		(12)		3,210		(35)
Mortgage-backed or related securities	47,247		2,843		—		50,090		—
	$	421,807	$	26,980	$	(106)	$	448,681	$	(94)

Accrued interest receivable on held-to-maturity debt securities was $3.3 million and $3.0 million as of December 31, 2021 and December 31, 2020, respectively, and was $10.1 million and $6.9 million on available-for-sale debt securities as of December 31, 2021 and December 31, 2020, respectively. Accrued interest receivable on securities is reported in accrued interest receivable on the Consolidated Statements of Financial Condition and is excluded from the calculation of the allowance for credit losses.

At December 31, 2021, the gross unrealized losses and the fair value for securities available-for-sale aggregated by the length of time that individual securities have been in a continuous unrealized loss position were as follows (in thousands):


	December 31, 2021
	Less Than 12 Months				12 Months or More				Total
	Fair Value		Unrealized Losses		Fair Value		Unrealized Losses		Fair Value		Unrealized Losses
Available-for-Sale:
U.S. Government and agency obligations	$	—	$	—	$	71,306	$	(621)	$	71,306	$	(621)
Municipal bonds	40,397		(221)		8,541		(99)		48,938		(320)
Corporate bonds	8,009		(121)		9,938		(62)		17,947		(183)
Mortgage-backed or related securities	1,307,411		(38,028)		721,454		(11,933)		2,028,865		(49,961)
Asset-backed securities	3,382		(9)		—		—		3,382		(9)

	$	1,359,199	$	(38,379)	$	811,239	$	(12,715)	$	2,170,438	$	(51,094)

At December 31, 2020, the gross unrealized losses and the fair value for securities available-for-sale and held-to-maturity aggregated by the length of time that individual securities have been in a continuous unrealized loss position were as follows (in thousands):


	December 31, 2020
	Less Than 12 Months				12 Months or More				Total
	Fair Value		Unrealized Losses		Fair Value		Unrealized Losses		Fair Value		Unrealized Losses
Available-for-Sale:
U.S. Government and agency obligations	$	3,126	$	(8)	$	50,603	$	(927)	$	53,729	$	(935)
Municipal bonds	495		(2)		—		—		495		(2)
Corporate bonds	3,586		(79)		—		—		3,586		(79)
Mortgage-backed or related securities	181,871		(1,046)		2,337		(14)		184,208		(1,060)
Asset-backed securities	—		—		5,676		(63)		5,676		(63)

	$	189,078	$	(1,135)	$	58,616	$	(1,004)	$	247,694	$	(2,139)

At December 31, 2021, there were 97 securities—available-for-sale with unrealized losses, compared to 54 at December 31, 2020. Management does not believe that any individual unrealized loss as of December 31, 2021 or December 31, 2020 resulted from credit loss. The decline in fair market value of these securities was generally due to changes in interest rates and changes in market-desired spreads subsequent to their purchase.

There were no sales of securities—trading for the years ended December 31, 2021, 2020 or 2019. There were no securities—trading in a nonaccrual status at December 31, 2021 or December 31, 2020. Net unrealized holding gains of $2.0 million were recognized in 2021 and net unrealized holding losses of $656,000 were recognized 2020.


	For the Year Ended December 31,
		2021		2020		2019
Available-for-Sale:
Gross Gains		$	993	$	899	$	239
Gross Losses		(495)		(445)		(205)
Balance, end of the period		$	498	$	454	$	34

During the year ended December 31, 2021, the Company sold one held-to-maturity security with a resulting net gain of $3,000 and had partial calls of securities that resulted in a net loss of $65,000. There were no sales of securities—held-to-maturity during the years ended December 31, 2020 or 2019, although there were partial calls of securities that resulted in a net gain of $216,000 for the year ended December 31, 2020 and a net loss of $1,000 for the year ended December 31, 2019. There were no securities—held-to-maturity in a nonaccrual status at December 31, 2021 and 2020.

During the year ended December 31, 2021, the Company sold a $4.8 million equity security with a resulting net gain of $46,000. There were two sales of equity securities totaling $1.06 billion for the year ended December 31, 2020 with a resulting net loss of $177,000 and no sales of equity securities during the year ended December 31, 2019. During the year ended December 31, 2020, the Company also sold Visa Class B stock with a net gain of $519,000. The stock was previously carried at a zero-cost basis due to transfer restrictions and uncertainty of litigation.

The amortized cost and estimated fair value of securities at December 31, 2021, by contractual maturity, are shown below (in thousands). Expected maturities will differ from contractual maturities because some securities may be called or prepaid with or without call or prepayment penalties.


	December 31, 2021
	Trading				Available-for-Sale				Held-to-Maturity
	Amortized Cost		Fair Value		Amortized Cost		Fair Value		Amortized Cost		Fair Value
Maturing within one year	$	—	$	—	$	14,077	$	14,174	$	12,026	$	12,087
Maturing after one year through five years	—		—		165,039		170,104		93,652		95,299
Maturing after five years through ten years	—		—		849,194		846,399		22,562		23,776
Maturing after ten years	27,203		26,981		2,624,850		2,608,316		393,115		410,691

	$	27,203	$	26,981	$	3,653,160	$	3,638,993	$	521,355	$	541,853

The following table presents, as of December 31, 2021, investment securities which were pledged to secure borrowings, public deposits or other obligations as permitted or required by law (in thousands):


	Carrying Value		Amortized Cost		Fair Value
Purpose or beneficiary:
State and local governments public deposits	$	209,304	$	208,827	$	221,319
Interest rate swap counterparties	24,268		23,723		24,285
Repurchase transaction accounts	292,700		300,441		292,700
Other	2,529		2,529		2,559
Total pledged securities	$	528,801	$	535,520	$	540,863

The Company monitors the credit quality of held-to-maturity debt securities through the use of credit rating. Credit ratings are reviewed and updated quarterly. The Company’s non-rated held-to-maturity debt securities are primarily United States government sponsored enterprise debentures carrying minimal to no credit risk. The remaining non-rated held-to-maturity debt securities balance is local municipal debt from within the Company’s geographic footprint and is monitored through quarterly or annual financial review. This municipal debt is predominately essential service or unlimited general obligation backed debt. The following tables summarize the amortized cost of held-to-maturity debt securities by credit rating at December 31, 2021 and December 31, 2020 (in thousands):


	December 31, 2021
	U.S. Government and agency obligations		Municipal bonds		Corporate bonds		Mortgage-backed or related securities		Total
AAA/AA/A	$	—	$	406,363	$	500	$	—	$	406,863

Not Rated	316		14,192		2,592		97,392		114,492


	$	316	$	420,555	$	3,092	$	97,392	$	521,355


	December 31, 2020
	U.S. Government and agency obligations		Municipal bonds		Corporate bonds		Mortgage-backed or related securities		Total
AAA/AA/A	$	—	$	349,123	$	500	$	—	$	349,623

Not Rated	340		21,875		2,722		47,247		72,184
	$	340	$	370,998	$	3,222	$	47,247	$	421,807

The following tables present the activity in the allowance for credit losses for held-to-maturity debt securities by major type for the year ended December 31, 2021 and December 31, 2020 (in thousands):