The following tables provide a summary of the amortized cost and fair values of the available-for-sale securities and held-to-maturity securities at June 30, 2021 and December 31, 2020 (in thousands):

	June 30, 2021
	Amortized Cost		Gross Unrealized Gains ⁽¹⁾		Gross Unrealized Losses ⁽¹⁾			Estimated Fair Value
Available-for-sale securities
U.S. government agency securities	$	3,148	$	32	$	—		$	3,180
State and municipal securities		2,384		46		—			2,430
Mortgage-backed securities:
Agency		1,000,745		14,825		(3,694	)		1,011,876
Commercial		77,413		3,171		(23	)		80,561
Non-agency		1,754		—		(2	)		1,752
Corporate fixed income securities		787,357		22,851		(639	)		809,569
Asset-backed securities		368,826		3,715		(1,752	)		370,789
	$	2,241,627	$	44,640	$	(6,110	)	$	2,280,157
Held-to-maturity securities ⁽²⁾
Asset-backed securities	$	4,987,612	$	10,399	$	(5,872	)	$	4,992,139

	December 31, 2020
	Amortized Cost		Gross Unrealized Gains ⁽¹⁾		Gross Unrealized Losses ⁽¹⁾			Estimated Fair Value
Available-for-sale securities
U.S. government agency securities	$	4,293	$	68	$	—		$	4,361
State and municipal securities		2,395		58		—			2,453
Mortgage-backed securities:
Agency		777,025		16,401		(16	)		793,410
Commercial		91,237		4,376		—			95,613
Non-agency		4,550		28		(9	)		4,569
Corporate fixed income securities		604,662		27,096		—			631,758
Asset-backed securities		700,177		3,522		(5,566	)		698,133
	$	2,184,339	$	51,549	$	(5,591	)	$	2,230,297
Held-to-maturity securities ⁽²⁾
Asset-backed securities	$	4,117,384	$	8,111	$	(17,535	)	$	4,107,960

We are required to evaluate our available-for-sale and held-to-maturity debt securities for any expected losses with recognition of an allowance for credit losses, when applicable. At June 30, 2021, we did not have an allowance for credit losses recorded on our investment portfolio.

Accrued interest receivable for our investment portfolio at June 30, 2021 and December 31, 2020 was $27.0 million and $26.0 million, respectively, and is reported in other assets in the consolidated statements of financial condition. We do not include reserves for interest receivable in the measurement of the allowance for credit losses.

During the first quarter of 2021, we transferred $312.9 million of certain asset-backed securities from available-for-sale to held-to-maturity. Management determined that it has both the positive intent and ability to hold these securities to maturity. The reclassification of these securities was accounted for at fair value. On the date of transfer, the difference between the par value and the fair value of these securities resulted in a premium or discount that, under amortized cost accounting, will be amortized as a yield adjustment to interest income using the interest method. There were no gains or losses recognized as a result of this transfer.

There were no sales of available-for-sale securities during the six months ended June 30, 2021. For the three and six months ended June 30, 2020, we received proceeds of $203.6 million and $491.9 million, respectively, from the sale of available-for-sale securities, which resulted in a realized gain of $0.2 million and a realized loss of $0.5 million for the three and six months ended June 30, 2020, respectively.

The table below summarizes the amortized cost and fair values of our securities by contractual maturity at June 30, 2021 and December 31, 2020 (in thousands). Expected maturities may differ significantly from contractual maturities, as issuers may have the right to call or prepay obligations with or without call or prepayment penalties.

	June 30, 2021				December 31, 2020
	Amortized Cost		Estimated Fair Value		Amortized Cost		Estimated Fair Value
Available-for-sale securities
Within one year	$	110,790	$	111,102	$	143,462	$	144,362
After one year through three years		200,105		206,467		134,040		137,625
After three years through five years		155,783		165,832		247,907		266,139
After five years through ten years		454,812		462,396		429,921		435,111
After ten years		1,320,137		1,334,360		1,229,009		1,247,060
	$	2,241,627	$	2,280,157	$	2,184,339	$	2,230,297
Held-to-maturity securities
After three years through five years	$	—	$	—	$	17,460	$	17,460
After five years through ten years		2,127,088		2,123,921		1,932,439		1,926,425
After ten years		2,860,524		2,868,218		2,167,485		2,164,075
	$	4,987,612	$	4,992,139	$	4,117,384	$	4,107,960

The maturities of our available-for-sale (fair value) and held-to-maturity (amortized cost) securities at June 30, 2021, are as follows (in thousands):

	Within 1 Year		1-5 Years		5-10 Years		After 10 Years		Total
Available-for-sale securities ⁽¹⁾
U.S. government agency securities	$	2,773	$	407	$	—	$	—	$	3,180
State and municipal securities		—		—		2,430		—		2,430
Mortgage-backed securities:
Agency		7		205		70,070		941,594		1,011,876
Commercial		3,765		4		—		76,792		80,561
Non-agency		1,130		—		—		622		1,752
Corporate fixed income securities		103,427		371,683		334,459		—		809,569
Asset-backed securities		—		—		55,437		315,352		370,789
	$	111,102	$	372,299	$	462,396	$	1,334,360	$	2,280,157
Held-to-maturity securities
Asset-backed securities	$	—	$	—	$	2,127,088	$	2,860,524	$	4,987,612

At June 30, 2021 and December 31, 2020, securities of $703.4 million and $368.4 million, respectively, were pledged at the Federal Home Loan Bank as collateral for borrowings and letters of credit obtained to secure public deposits. At June 30, 2021 and December 31, 2020, securities of $1.2 billion and $1.4 billion, respectively, were pledged with the Federal Reserve discount window.

The following table shows the gross unrealized losses and fair value of the Company’s investment securities with unrealized losses, aggregated by investment category and length of time the individual investment securities have been in continuous unrealized loss positions, at June 30, 2021 (in thousands):

	Less than 12 months					12 months or more					Total
	Gross Unrealized Losses			Estimated Fair Value		Gross Unrealized Losses			Estimated Fair Value		Gross Unrealized Losses			Estimated Fair Value
Available-for-sale securities
Mortgage-backed securities:
Agency	$	(3,694	)	$	203,147	$	—		$	—	$	(3,694	)	$	203,147
Commercial		(23	)		3,765		—			—		(23	)		3,765
Non-agency		—			—		(2	)		621		(2	)		621
Corporate fixed income securities		(639	)		88,265		—			—		(639	)		88,265
Asset-backed securities		(485	)		29,150		(1,267	)		144,890		(1,752	)		174,040
	$	(4,841	)	$	324,327	$	(1,269	)	$	145,511	$	(6,110	)	$	469,838

At June 30, 2021, the amortized cost of 34 securities classified as available for sale exceeded their fair value by $6.1 million, of which $1.3 million related to investment securities that had been in a loss position for 12 months or longer. The total fair value of these investments at June 30, 2021, was $469.8 million, which was 20.6% of our available-for-sale portfolio.

The Company uses Moody credit ratings as the primary credit quality indicator for its held-to-maturity debt securities. Each security is evaluated at least quarterly. The indicators represent the rating for debt securities, as of the date presented, based on the most recent assessment performed. The following table shows the amortized cost of our held-to-maturity securities by credit quality indicator at June 30, 2021 (in thousands):

	AAA		AA		A		C		Total
Held-to-maturity securities
Asset-backed securities	$	1,116,155	$	3,864,016	$	5,000	$	2,441	$	4,987,612