The amortized cost, gross unrealized gains and losses, and fair value of available for sale securities as of March 31, 2021 and December 31, 2020 were as follows:


	As of March 31, 2021
	Amortized Cost		Unrealized Gains		Unrealized Losses		Fair Value
	(In Thousands)
Debt securities:
Government-sponsored residential mortgage-backed securities	$	2,713,898	$	23,199	$	(45,395)	$	2,691,702
Government-sponsored commercial mortgage-backed securities	119,064		—		(2,793)		116,271
U.S. Agency bonds	860,554		—		(28,882)		831,672
U.S. Treasury securities	69,385		30		(325)		69,090
State and municipal bonds and obligations	260,818		16,700		—		277,518
	$	4,023,719	$	39,929	$	(77,395)	$	3,986,253


	As of December 31, 2020
	Amortized Cost		Unrealized Gains		Unrealized Losses		Fair Value
	(In Thousands)
Debt securities:
Government-sponsored residential mortgage-backed securities	$	2,106,658	$	42,142	$	—	$	2,148,800
Government-sponsored commercial mortgage-backed securities	17,054		27		—		17,081
U.S. Agency bonds	670,468		113		(3,872)		666,709
U.S. Treasury securities	70,106		263		—		70,369
State and municipal bonds and obligations	260,898		20,004		—		280,902
	$	3,125,184	$	62,549	$	(3,872)	$	3,183,861

The amortized cost and estimated fair value of available for sale securities by contractual maturities as of March 31, 2021 and December 31, 2020 are shown below. Actual maturities may differ from contractual maturities because borrowers may have the right to call or prepay obligations with or without prepayment penalties.


	As of March 31, 2021
	Due in one year or less				Due after one year to five years				Due after five to ten years				Due after ten years				Total
	Amortized Cost		Fair Value		Amortized Cost		Fair Value		Amortized Cost		Fair Value		Amortized Cost		Fair Value		Amortized Cost		Fair Value
	(In Thousands)
Government-sponsored residential mortgage-backed securities	$	—	$	—	$	20,503	$	21,777	$	87,383	$	91,340	$	2,606,012	$	2,578,585	$	2,713,898	$	2,691,702
Government-sponsored commercial mortgage-backed securities	—		—		24,090		23,771		94,974		92,500		—		—		119,064		116,271
U.S. Agency bonds	—		—		99,784		98,111		760,770		733,561		—		—		860,554		831,672
U.S. Treasury securities	10,065		10,095		59,320		58,995		—		—		—		—		69,385		69,090
State and municipal bonds and obligations	405		406		25,244		26,220		72,587		76,077		162,582		174,815		260,818		277,518
Total	$	10,470	$	10,501	$	228,941	$	228,874	$	1,015,714	$	993,478	$	2,768,594	$	2,753,400	$	4,023,719	$	3,986,253


	As of December 31, 2020
	Due in one year or less				Due after one year to five years				Due after five to ten years				Due after ten years				Total
	Amortized Cost		Fair Value		Amortized Cost		Fair Value		Amortized Cost		Fair Value		Amortized Cost		Fair Value		Amortized Cost		Fair Value
	(In Thousands)
Government-sponsored residential mortgage-backed securities	$	—	$	—	$	46,293	$	48,925	$	96,338	$	100,278	$	1,964,027	$	1,999,597	$	2,106,658	$	2,148,800
Government-sponsored commercial mortgage-backed securities	—		—		—		—		17,054		17,081		—		—		17,054		17,081
U.S. Agency bonds	—		—		99,772		99,834		570,696		566,875		—		—		670,468		666,709
U.S. Treasury securities	50,023		50,251		20,083		20,118		—		—		—		—		70,106		70,369
State and municipal bonds and obligations	406		408		20,511		21,431		74,980		79,635		165,001		179,428		260,898		280,902
Total	$	50,429	$	50,659	$	186,659	$	190,308	$	759,068	$	763,869	$	2,129,028	$	2,179,025	$	3,125,184	$	3,183,861

Gross realized gains from sales of available for sale securities during the three months ended March 31, 2021 and 2020 were $1.2 million and $0.1 million, respectively. There were no significant gross realized losses from sales of securities available for sale during the three months ended March 31, 2021 and 2020. There was no other-than-temporary impairment (“OTTI”) recorded during the three months ended March 31, 2021 and 2020.

Management prepares an estimate of the expected cash flows for investment securities available for sale that potentially may be deemed to have been an OTTI. This estimate begins with the contractual cash flows of the security. This amount is then reduced by an estimate of probable credit losses associated with the security. When estimating the extent of probable losses on the securities, management considers the credit quality and the ability to pay of the underlying issuers. Indicators of diminished credit quality of the issuers include defaults, interest deferrals, or “payments in kind.” Management also considers those factors listed in the “Investments – Debt and Equity Securities” topic of the FASB ASC when estimating the ultimate realizability of the cash flows for each individual security.

The resulting estimate of cash flows after considering credit is then subject to a present value computation using a discount rate equal to the current yield used to accrete the beneficial interest or the effective interest rate implicit in the security at the date of acquisition. If the present value of the estimated cash flows is less than the current amortized cost basis, an OTTI is considered to have occurred and the security is written down to the fair value indicated by the cash flow analysis. As part of the analysis, management considers whether it intends to sell the security or whether it is more than likely that it would be required to sell the security before the expected recovery of its amortized cost basis.

Information pertaining to available for sale securities with gross unrealized losses as of March 31, 2021 and December 31, 2020, which the Company has not deemed to be OTTI, aggregated by investment category and length of time that individual securities have been in a continuous loss position, follows:


	As of March 31, 2021
		Less than 12 Months				12 Months or Longer				Total
	# of Holdings	Gross Unrealized Losses		Fair Value		Gross Unrealized Losses		Fair Value		Gross Unrealized Losses		Fair Value
	(Dollars in thousands)
Government-sponsored residential mortgage-backed securities	18	$	45,395	$	2,004,883	$	—	$	—	$	45,395	$	2,004,883
Government-sponsored commercial mortgage-backed securities	7	2,793		116,271		—		—		2,793		116,271
U.S. Agency bonds	13	28,882		831,672		—		—		28,882		831,672
U.S. Treasury securities	2	325		58,995		—		—		325		58,995
	40	$	77,395	$	3,011,821	$	—	$	—	$	77,395	$	3,011,821


	As of December 31, 2020
		Less than 12 Months				12 Months or Longer				Total
	# of Holdings	Gross Unrealized Losses		Fair Value		Gross Unrealized Losses		Fair Value		Gross Unrealized Losses		Fair Value
	(Dollars in thousands)
U.S. Agency bonds	6	3,872		416,824		—		—		3,872		416,824
	6	$	3,872	$	416,824	$	—	$	—	$	3,872	$	416,824

The Company does not intend to sell these investments and has determined based upon available evidence that it is more likely than not that the Company will not be required to sell each security before the expected recovery of its amortized cost basis. As a result, the Company does not consider these investments with gross unrealized losses to be OTTI. The Company made this determination by reviewing various qualitative and quantitative factors regarding each investment category, such as current market conditions, extent and nature of changes in fair value, issuer rating changes and trends, and volatility of earnings.

As a result of the Company’s review of these qualitative and quantitative factors, the causes of the impairments listed in the tables above by category are as follows as of March 31, 2021 and December 31, 2020:

•Government-sponsored residential mortgage-backed securities – The securities with unrealized losses in this portfolio have contractual terms that generally do not permit the issuer to settle the security at a price less than the current par value of the investment. The decline in market value of these securities is attributable to changes in interest rates and not credit quality. Additionally, these securities are implicitly guaranteed by the U.S. government or one of its agencies.

•Government-sponsored commercial mortgage-backed securities – The securities with unrealized losses in this portfolio have contractual terms that generally do not permit the issuer to settle the security at a price less than the current par value of the investment. The decline in market value of these securities is attributable to changes in interest rates and not credit quality. Additionally, these securities are implicitly guaranteed by the U.S. government or one of its agencies.

•U.S. Agency bonds – The securities with unrealized losses in this portfolio have contractual terms that generally do not permit the issuer to settle the security at a price less than the current par value of the investment. The decline in market value of these securities is attributable to changes in interest rates and not credit quality. The securities in a loss position as of December 31, 2020 remain in a loss position as of March 31, 2021 but have not yet been held for a period of 12 months or longer as of March 31, 2021. Additionally, these securities are implicitly guaranteed by the U.S. government or one of its agencies.

•U.S. Treasury securities – The securities with unrealized losses in this portfolio have contractual terms that generally do not permit the issuer to settle the securities at a price less than the current par value of the investments. The decline in market value of these securities is attributable to changes in interest rates and not credit quality. Additionally, these securities are implicitly guaranteed by the U.S. government or one of its agencies.