
(In thousands)	2020		2019
Available for sale debt securities	$	12,449,264	$	8,571,626
Trading debt securities	35,321		28,161
Equity securities:
Readily determinable fair value	2,966		2,929
No readily determinable fair value	1,397		1,280
Other:
Federal Reserve Bank stock	34,070		33,770
Federal Home Loan Bank stock	10,307		10,000
Equity method investments	18,000		—
Private equity investments	94,368		94,122
Total investment securities (1)	$	12,645,693	$	8,741,888

The Company has elected to measure equity securities with no readily determinable fair value at cost minus impairment, if any, plus or minus changes resulting from observable price changes for the identical or similar investment of the same issuer. This portfolio includes the Company's holdings of Visa Class B shares, which have a carrying value of zero, as there have not been observable price changes in orderly transactions for identical or similar investments of the same issuer. During the year-ended December 31, 2020, the Company did not record any impairment or other adjustments to the carrying amount of its portfolio of equity securities with no readily determinable fair value.

Other investment securities include Federal Reserve Bank (FRB) stock, Federal Home Loan Bank (FHLB) stock, equity method investments, and investments in portfolio concerns held by the Company's private equity subsidiary. FRB stock and FHLB stock are held for debt and regulatory purposes. Investment in FRB stock is based on the capital structure of the investing bank, and investment in FHLB stock is tied to the level of borrowings from the FHLB. These holdings are carried at cost. The Company's equity method investments are carried at cost, adjusted to reflect the Company's portion of income, loss, or dividends of the investee. The private equity investments, in the absence of readily ascertainable market values, are carried at estimated fair value.

The majority of the Company’s investment portfolio is comprised of available for sale debt securities, which are carried at fair value with changes in fair value reported in accumulated other comprehensive income (AOCI). A summary of the available for sale debt securities by maturity groupings as of December 31, 2020 is shown in the following table. The weighted average yield for each range of maturities was calculated using the yield on each security within that range weighted by the amortized cost of each security at December 31, 2020. Yields on tax exempt securities have not been adjusted for tax exempt status. The investment portfolio includes agency mortgage-backed securities, which are guaranteed by agencies such as FHLMC, FNMA, and GNMA, in addition to non-agency mortgage-backed securities, which have no guarantee but are collateralized by commercial and residential mortgages. Also included are certain other asset-backed securities, which are primarily collateralized by credit cards, automobiles, student loans, and commercial loans. These securities differ from traditional debt securities primarily in that they may have uncertain maturity dates and are priced based on estimated prepayment rates on the underlying collateral.


(Dollars in thousands)	Amortized Cost		Fair Value		Weighted Average Yield
U.S. government and federal agency obligations:
Within 1 year	$	59,627	$	59,641	.90	*%
After 1 but within 5 years	490,333		521,540		2.22	*
After 5 but within 10 years	225,632		256,878		.65	*

Total U.S. government and federal agency obligations	775,592		838,059		1.66	*
Government-sponsored enterprise obligations:
Within 1 year	14,993		14,916		2.15


After 10 years	35,810		39,569		2.39
Total government-sponsored enterprise obligations	50,803		54,485		2.32
State and municipal obligations:
Within 1 year	34,694		34,866		2.35
After 1 but within 5 years	865,165		901,201		2.20
After 5 but within 10 years	595,510		627,063		2.01
After 10 years	472,637		481,969		1.84
Total state and municipal obligations	1,968,006		2,045,099		2.06
Mortgage and asset-backed securities:
Agency mortgage-backed securities	6,557,098		6,712,085		2.00
Non-agency mortgage-backed securities	358,074		361,074		2.39
Asset-backed securities	1,853,791		1,882,243		1.53
Total mortgage and asset-backed securities	8,768,963		8,955,402		1.92
Other debt securities:
Within 1 year	8,041		8,118
After 1 but within 5 years	254,173		265,486
After 5 but within 10 years	240,759		250,036
After 10 years	31,196		32,579
Total other debt securities	534,169		556,219
Total available for sale debt securities	$	12,097,533	$	12,449,264

Investments in U.S. government and federal agency obligations include U.S. Treasury inflation-protected securities, which totaled $434.6 million, at fair value, at December 31, 2020. Interest paid on these securities increases with inflation and decreases with deflation, as measured by the Consumer Price Index. At maturity, the principal paid is the greater of an inflation-adjusted principal or the original principal.

As described in Note 1, the Company adopted ASU 2016-13, Measurement of Credit Losses on Financial Instruments, on January 1, 2020. The adoption of ASU 2016-13 had no impact to the Company's available for sale securities reported in its consolidated financial statements at January 1, 2020. For the year ended December 31, 2020, the Company did not recognize a credit loss expense on any available for sale debt securities.

The Company’s model for establishing its allowance for credit losses uses cash flows projected to be received over the estimated life of the securities, discounted to present value, and compared to the current amortized cost bases of the securities. Securities for which fair value is less than amortized cost are reviewed for impairment. Special emphasis is placed on securities whose credit rating has fallen below Baa3 (Moody's) or BBB- (Standard & Poor's), whose fair values have fallen more than 20% below purchase price, or who have been identified based on management’s judgment. These securities are placed on a watch list and cash flow analyses are prepared on an individual security basis. Credit impairment is determined using input factors such as cash flow projections, contractual payments required, expected delinquency rates, credit support from other tranches, prepayment speeds, collateral loss severity rates (including loan to values), and various other information related to

Significant inputs to the cash flow model used at December 31, 2020 to quantify credit losses were primarily credit support agreements, as the securities on the Company's watch list at December 31, 2020 were securities backed by government-guaranteed student loans and are expected to perform as contractually required. As of December 31, 2020, the Company did not identify any securities for which a credit loss exists.

The table below summarizes debt securities available for sale in an unrealized loss position, aggregated by length of impairment period, for which an allowance for credit losses has not been recorded at December 31, 2020. Unrealized losses on these available for sale securities have not been recognized into income because after review, the securities were deemed not to be impaired. The unrealized losses on these securities are primarily attributable to changes in interest rates and current market conditions. Additionally, management does not intend to sell the securities, and it is more likely than not that management will not be required to sell the securities prior to their anticipated recovery.


	Less than 12 months				12 months or longer				Total
(In thousands)	Fair Value		Unrealized Losses		Fair Value		Unrealized Losses		Fair Value		Unrealized Losses
December 31, 2020

Government-sponsored enterprise obligations	$	19,720	$	98	$	—	$	—	$	19,720	$	98
State and municipal obligations	45,622		230		—		—		45,622		230
Mortgage and asset-backed securities:
Agency mortgage-backed securities	470,373		2,802		—		—		470,373		2,802
Non-agency mortgage-backed securities	112,861		380		—		—		112,861		380
Asset-backed securities	21,360		56		253,734		2,617		275,094		2,673
Total mortgage and asset-backed securities	604,594		3,238		253,734		2,617		858,328		5,855
Other debt securities	24,522		175		—		—		24,522		175
Total	$	694,458	$	3,741	$	253,734	$	2,617	$	948,192	$	6,358


	Less than 12 months				12 months or longer				Total
(In thousands)	Fair Value		Unrealized Losses		Fair Value		Unrealized Losses		Fair Value		Unrealized Losses
December 31, 2019
U.S. government and federal agency obligations	$	31,787	$	21	$	25,405	$	21	$	57,192	$	42
Government-sponsored enterprise obligations	6,155		187		—		—		6,155		187
State and municipal obligations	6,700		31		1,554		1		8,254		32
Mortgage and asset-backed securities:
Agency mortgage-backed securities	652,352		5,306		147,653		867		800,005		6,173
Non-agency mortgage-backed securities	102,931		254		189,747		451		292,678		705
Asset-backed securities	330,876		3,610		152,461		2,108		483,337		5,718
Total mortgage and asset-backed securities	1,086,159		9,170		489,861		3,426		1,576,020		12,596
Other debt securities	5,496		4		997		3		6,493		7
Total	$	1,136,297	$	9,413	$	517,817	$	3,451	$	1,654,114	$	12,864

The entire available for sale debt portfolio included $948.2 million of securities that were in a loss position at December 31, 2020, compared to $1.7 billion at December 31, 2019. The total amount of unrealized loss on these securities was $6.4 million at December 31, 2020, a decrease of $6.5 million compared to the loss at December 31, 2019. Securities with significant unrealized losses are discussed in the "Allowance for credit losses on available for sale debt securities" section above.

For debt securities classified as available for sale, the following table shows the amortized cost, fair value, and allowance for credit losses of securities available for sale at December 31, 2020 and the corresponding amounts of gross unrealized gains and losses (pre-tax) in AOCI, by security type.


(In thousands)	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses		Allowance for Credit Losses		Fair Value
December 31, 2020
U.S. government and federal agency obligations	$	775,592	$	62,467	$	—	$	—	$	838,059
Government-sponsored enterprise obligations	50,803		3,780		(98)		—		54,485
State and municipal obligations	1,968,006		77,323		(230)		—		2,045,099
Mortgage and asset-backed securities:
Agency mortgage-backed securities	6,557,098		157,789		(2,802)		—		6,712,085
Non-agency mortgage-backed securities	358,074		3,380		(380)		—		361,074
Asset-backed securities	1,853,791		31,125		(2,673)		—		1,882,243
Total mortgage and asset-backed securities	8,768,963		192,294		(5,855)		—		8,955,402
Other debt securities	534,169		22,225		(175)		—		556,219
Total	$	12,097,533	$	358,089	$	(6,358)	$	—	$	12,449,264

For debt securities classified as available for sale, the following table shows the amortized cost and fair value of securities available for sale at December 31, 2019 and the corresponding amounts of gross unrealized gains and losses (pre-tax) in AOCI, by security type.


(In thousands)	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses		Fair Value
December 31, 2019
U.S. government and federal agency obligations	$	827,861	$	23,957	$	(42)	$	851,776
Government-sponsored enterprise obligations	138,734		730		(187)		139,277
State and municipal obligations	1,225,532		42,427		(32)		1,267,927
Mortgage and asset-backed securities:
Agency mortgage-backed securities	3,893,247		50,890		(6,173)		3,937,964
Non-agency mortgage-backed securities	796,451		14,036		(705)		809,782
Asset-backed securities	1,228,151		11,056		(5,718)		1,233,489
Total mortgage and asset-backed securities	5,917,849		75,982		(12,596)		5,981,235
Other debt securities	325,555		5,863		(7)		331,411
Total	$	8,435,531	$	148,959	$	(12,864)	$	8,571,626


	For the Year Ended December 31
(In thousands)	2020		2019		2018
Proceeds from sales of securities:
Available for sale debt securities	$	602,475	$	402,103	$	667,227
Equity securities	2		3,856		41,637
Other	—		7,244		—
Total proceeds	$	602,477	$	413,203	$	708,864

Investment securities gains (losses), net:
Available for sale debt securities:

Gains realized on sales	$	21,096	$	2,354	$	448
Losses realized on sales	—		(2,568)		(10,101)
Other-than-temporary impairment recognized on debt securities	—		(133)		(68)
Equity securities:

Gains realized on sales	2		3,262		1,759
Losses realized on sales	—		—		(8,917)
Fair value adjustments, net	37		344		2,542
Other:
Gains realized on sales	—		1,094		—

Fair value adjustments, net	(10,103)		(727)		13,849
Total investment securities gains (losses), net	$	11,032	$	3,626	$	(488)

Net gains and losses on investment securities for the year ended December 31, 2020 included net gains of $21.1 million realized on sales of available for sale debt securities and net losses in fair value of $10.1 million on private equity investments due to fair value adjustments.

At December 31, 2020 securities totaling $4.8 billion in fair value were pledged to secure public fund deposits, securities sold under agreements to repurchase, trust funds, and borrowings at the FRB and FHLB, compared to $4.3 billion at December 31, 2019. Securities pledged under agreements pursuant to which the collateral may be sold or re-pledged by the secured parties approximated $214.2 million, while the remaining securities were pledged under agreements pursuant to which the secured parties may not sell or re-pledge the collateral. Except for obligations of various government-sponsored enterprises such as FNMA, FHLB and FHLMC, no investment in a single issuer exceeds 10% of stockholders’ equity.