
September 30, 2023	Amortized Cost		Allowance for Credit Losses		Net Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses		Estimated Fair Value
Available-for-Sale:
U.S. Treasury notes	$	250.1	$	—	$	250.1	$	—	$	(34.2)	$	215.9
State, county, and municipal securities	257.5		—		257.5		—		(54.9)		202.6
Obligations of U.S. government agencies	179.3		—		179.3		—		(17.3)		162.0
U.S. agency commercial mortgage-backed securities	1,191.9		—		1,191.9		0.1		(125.1)		1,066.9
U.S. agency residential mortgage-backed securities	1,474.3		—		1,474.3		—		(189.3)		1,285.0
Collateralized mortgage obligations	1,302.9		—		1,302.9		—		(159.2)		1,143.7
Private mortgage-backed securities	246.4		—		246.4		—		(39.1)		207.3
Collateralized loan obligations	1,126.7		—		1,126.7		—		(8.9)		1,117.8
Corporate securities	261.1		—		261.1		—		(34.6)		226.5

Total	$	6,290.2	$	—	$	6,290.2	$	0.1	$	(662.6)	$	5,627.7


September 30, 2023	Amortized Cost1		Allowance for Credit Losses		Net Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses		Estimated Fair Value
Held-to-Maturity:
U.S. Treasury notes	$	398.4	$	—	$	398.4	$	—	$	(6.8)	$	391.6
State, county, and municipal securities	179.0		—		179.0		—		(34.9)		144.1
Obligations of U.S. government agencies	353.8		—		353.8		—		(59.5)		294.3
U.S. agency commercial mortgage-backed securities	515.2		—		515.2		—		(71.9)		443.3
U.S. agency residential mortgage-backed securities	1,269.8		—		1,269.8		—		(197.2)		1,072.6
Collateralized mortgage obligations	487.1		—		487.1		—		(86.2)		400.9
Corporate securities	57.0		(0.8)		56.2		—		(6.9)		49.3

Total	$	3,260.3	$	(0.8)	$	3,259.5	$	—	$	(463.4)	$	2,796.1
(1) Amortized cost presented above includes $11.4 million of unamortized gains in U.S. agency residential and commercial mortgage-backed securities and collateralized mortgage obligations related to the 2021 transfer of securities from available-for-sale to held-to-maturity, and $18.6 million of unamortized losses in state, county, and municipal, obligations of U.S. government agencies and collateralized loan obligations related to the 2022 transfer of securities from available-for-sale to held-to-maturity.


December 31, 2022	Amortized Cost		Allowance for Credit Losses		Net Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses		Estimated Fair Value
Available-for-Sale:
U.S. Treasury notes	$	675.1	$	—	$	675.1	$	2.1	$	(34.5)	$	642.7
State, county, and municipal securities	314.3		—		314.3		—		(50.6)		263.7
Obligations of U.S. government agencies	216.2		—		216.2		—		(17.3)		198.9
U.S. agency commercial mortgage-backed securities	1,468.0		—		1,468.0		0.2		(117.0)		1,351.2
U.S. agency residential mortgage-backed securities	1,726.0		—		1,726.0		—		(167.7)		1,558.3
Collateralized mortgage obligations	1,491.5		—		1,491.5		—		(141.3)		1,350.2
Private mortgage-backed securities	264.9		—		264.9		—		(36.9)		228.0
Collateralized loan obligations	1,145.2		—		1,145.2		—		(33.6)		1,111.6
Corporate securities	272.3		—		272.3		—		(30.8)		241.5

Total	$	7,573.5	$	—	$	7,573.5	$	2.3	$	(629.7)	$	6,946.1


December 31, 2022	Amortized Cost1		Allowance for Credit Losses		Net Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses		Estimated Fair Value
Held-to-Maturity:
U.S. Treasury notes	$	396.6	$	—	$	396.6	$	—	$	(10.2)	$	386.4
State, county, and municipal securities	181.2		(0.1)		181.1		0.2		(31.6)		149.7
Obligations of U.S. government agencies	351.7		—		351.7		—		(49.6)		302.1
U.S. agency commercial mortgage-backed securities	526.8		—		526.8		—		(58.3)		468.5
U.S. agency residential mortgage-backed securities	1,391.5		—		1,391.5		—		(166.6)		1,224.9
Collateralized mortgage obligations	525.8		—		525.8		0.2		(76.7)		449.3
Corporate securities	80.1		(1.8)		78.3		—		(7.0)		71.3

Total	$	3,453.7	$	(1.9)	$	3,451.8	$	0.4	$	(400.0)	$	3,052.2
(1) Amortized cost presented above includes $20.2 million of unamortized losses and of $14.2 million unamortized gains related to the 2021 and 2022 transfer of securities from available-for-sale to held-to-maturity.

The following tables show the gross unrealized losses and fair values of available-for-sale investment securities and the length of time individual investment securities have been in an unrealized loss position as of September 30, 2023 and December 31, 2022.


	Less than 12 Months				12 Months or More				Total
September 30, 2023	Fair Value		Gross Unrealized Losses		Fair Value		Gross Unrealized Losses		Fair Value		Gross Unrealized Losses
Available-for-Sale:
U.S. Treasury notes	$	—	$	—	$	215.9	$	(34.2)	$	215.9	$	(34.2)
State, county, and municipal securities	1.0		—		199.7		(54.9)		200.7		(54.9)
Obligations of U.S. government agencies	—		—		161.5		(17.3)		161.5		(17.3)
U.S. agency commercial mortgage-backed securities	0.3		—		1,057.8		(125.1)		1,058.1		(125.1)
U.S. agency residential mortgage-backed securities	0.9		—		1,284.0		(189.3)		1,284.9		(189.3)
Collateralized mortgage obligations	—		—		1,143.7		(159.2)		1,143.7		(159.2)
Private mortgage-backed securities	—		—		207.3		(39.1)		207.3		(39.1)
Collateralized loan obligations	—		—		1,117.8		(8.9)		1,117.8		(8.9)
Corporate securities	—		—		226.6		(34.6)		226.6		(34.6)

Total	$	2.2	$	—	$	5,614.3	$	(662.6)	$	5,616.5	$	(662.6)


	Less than 12 Months				12 Months or More				Total
December 31, 2022	Fair Value		Gross Unrealized Losses		Fair Value		Gross Unrealized Losses		Fair Value		Gross Unrealized Losses
Available-for-Sale:
U.S. Treasury notes	$	168.8	$	(4.7)	$	170.4	$	(29.8)	$	339.2	$	(34.5)
State, county, and municipal securities	104.9		(9.0)		146.1		(41.6)		251.0		(50.6)
Obligations of U.S. government agencies	152.2		(10.1)		46.1		(7.2)		198.3		(17.3)
U.S. agency commercial mortgage-backed securities	1,069.8		(59.9)		270.8		(57.0)		1,340.6		(116.9)
U.S. agency residential mortgage-backed securities	1,213.5		(112.3)		344.6		(55.4)		1,558.1		(167.7)
Collateralized mortgage obligations	1,016.4		(90.1)		333.0		(51.3)		1,349.4		(141.4)
Private mortgage-backed securities	133.1		(19.1)		94.9		(17.8)		228.0		(36.9)
Collateralized loan obligations	1,082.6		(33.1)		28.9		(0.5)		1,111.5		(33.6)
Corporate securities	130.6		(8.3)		110.8		(22.5)		241.4		(30.8)

Total	$	5,071.9	$	(346.6)	$	1,545.6	$	(283.1)	$	6,617.5	$	(629.7)

The Company determines credit losses on both available-for-sale and held-to-maturity investment securities by a discounted cash flow approach using the security’s effective interest rate at the time of purchase or upon acquisition. The allowance for credit losses is measured as the amount by which an investment security’s amortized cost exceeds the net present value of expected future cash flows. However, the amount of credit losses for available-for-sale investment securities is limited to the amount of a security’s unrealized loss. Credit losses on held-to-maturity investment securities are representative of current expected credit losses that management expects to be incurred over the life of the investment. The allowance for credit losses is established through a charge to provision for credit losses in current period earnings.

The available-for-sale securities portfolio primarily contains securities that are guaranteed by a sovereign entity or are generally considered to have non-credit related risks, such as interest rate risk or prepayment and liquidity factors. The Company considers whether the securities are issued by the federal government or its agencies and whether downgrades by bond rating agencies have occurred.

As of September 30, 2023 and December 31, 2022, the Company had 1,034 and 1,222 individual investment securities, respectively, that were in an unrealized loss position, which was related primarily to fluctuations in current interest rates. As of September 30, 2023, the Company had the intent and ability to hold these investment securities for a period of time sufficient to allow for an anticipated recovery. The Company does not intend to sell any of the available-for-sale securities in the above table, and the Company does not anticipate it will have to sell any securities before a recovery in cost.


The following table presents the activity in the allowance for credit losses related to available-for-sale investment securities:

	Three Months Ended September 30,				Nine Months Ended September 30,
	2023		2022		2023		2022
Beginning balance	$	1.4	$	—	$	—	$	—
(Reduction of) provision for credit losses	(1.4)		—		—		—
Ending balance	$	—	$	—	$	—	$	—

The following table presents the activity in the allowance for credit losses related to held-to-maturity investment securities:

	Three Months Ended September 30,				Nine Months Ended September 30,
	2023		2022		2023		2022
Beginning balance	$	0.7	$	1.6	$	1.9	$	—
Provision for (reduction of) credit losses	0.1		0.3		(1.1)		1.9
Ending balance	$	0.8	$	1.9	$	0.8	$	1.9

The Company had no allowance for credit losses for available-for-sale corporate investment securities as of September 30, 2023 and December 31, 2022, respectively. The Company had a $0.8 million and a $1.9 million allowance for credit losses for held-to-maturity corporate and state, county, and municipal investment securities as of September 30, 2023 and December 31, 2022, respectively.


September 30, 2023	AAA		AA		A		BBB		BB		Not Rated		Total
U.S. Treasury notes	$	398.4	$	—	$	—	$	—	$	—	$	—	$	398.4
State, county, and municipal securities	68.1		92.3		10.6		—		—		8.0		179.0
Obligations of U.S. government agencies	353.8		—		—		—		—		—		353.8
U.S. agency commercial mortgage-backed securities
FNMA/FHLMC	360.9		—		—		—		—		—		360.9
GNMA	154.3		—		—		—		—		—		154.3
U.S. agency residential mortgage-backed securities
FNMA/FHLMC	1,225.6		—		—		—		—		—		1,225.6
GNMA	44.2		—		—		—		—		—		44.2
Collateralized mortgage obligations
FNMA/FHLMC	342.0		—		—		—		—		—		342.0
GNMA	145.1		—		—		—		—		—		145.1
Corporate securities	—		—		—		47.0		5.0		5.0		57.0

Total	$	3,092.4	$	92.3	$	10.6	$	47.0	$	5.0	$	13.0	$	3,260.3


December 31, 2022	AAA		AA		A		BBB		BB		Not Rated		Total
U.S. Treasury notes	$	396.6	$	—	$	—	$	—	$	—	$	—	$	396.6
State, county, and municipal securities	68.3		92.8		11.5		—		—		8.6		181.2
Obligations of U.S. government agencies	351.7		—		—		—		—		—		351.7
U.S. agency commercial mortgage-backed securities
FNMA/FHLMC	364.9		—		—		—		—		—		364.9
GNMA	161.9		—		—		—		—		—		161.9
U.S. agency residential mortgage-backed securities
FNMA/FHLMC	1,342.9		—		—		—		—		—		1,342.9
GNMA	48.6		—		—		—		—		—		48.6
Collateralized mortgage obligations
FNMA/FHLMC	525.8		—		—		—		—		—		525.8
Corporate securities	—		—		—		65.1		10.0		5.0		80.1

Total	$	3,260.7	$	92.8	$	11.5	$	65.1	$	10.0	$	13.6	$	3,453.7

As of September 30, 2023 and December 31, 2022, the Company had $36.5 million and $38.9 million, respectively, of accrued interest receivable from investment securities on the consolidated balance sheets. Accrued interest receivable is presented as a separate line item on the consolidated balance sheets and the Company does not include accrued interest receivable in the carrying amount of financial assets held at the amortized cost basis or in the related allowance for credit losses calculation.

There were no material gross realized gains and no material gross realized losses during the three months ended September 30, 2023. During the nine months ended September 30, 2023, there were no material gross realized gains and $23.5 million in gross realized losses on the disposition of available-for-sale investment securities, as a result of the sale of $853.0 million in carrying value of investment securities. For the three and the nine month periods ended September 30, 2022, there were no material gross realized gains and $46.3 million of gross realized losses on the disposition of available-for-sale investment securities.

Maturities of securities do not reflect rate repricing opportunities present in adjustable-rate mortgage-backed securities. Maturities of mortgage-backed securities have been adjusted to reflect shorter maturities based upon estimated prepayments of principal. All other investment securities maturities are shown at contractual maturity dates.


	Available-for-Sale				Held-to-Maturity
September 30, 2023	Amortized Cost		Estimated Fair Value		Amortized Cost		Estimated Fair Value
Within one year	$	1.6	$	1.5	$	308.7	$	304.5
After one year but within five years	1,036.0		941.3		346.4		320.2
After five years but within ten years	1,387.9		1,220.0		654.8		551.5
After ten years	3,864.7		3,464.9		1,950.4		1,619.9
Total	$	6,290.2	$	5,627.7	$	3,260.3	$	2,796.1

As of September 30, 2023, the Company held investment securities callable within one year having amortized costs and estimated fair values of $1,592.1 million and $1,514.4 million, respectively. These investment securities are primarily included in the “after ten years” category in the table above. As of September 30, 2023, the Company had no callable structured notes.

As of September 30, 2023 and December 31, 2022, the Company had amortized costs of $7,066.8 million and $4,998.9 million, respectively, for investment securities pledged to secure public deposits, securities sold under repurchase agreements, and as collateral for FHLB and the FRB term funding program line capacity that had estimated fair values of $6,169.7 million and $4,432.0 million, as of September 30, 2023 and December 31, 2022, respectively. All securities sold under repurchase agreements are with clients and mature on the next banking day. The Company retains possession of the underlying securities sold under repurchase agreements.

As of September 30, 2023 and December 31, 2022, the Company held $189.5 million and $198.6 million, respectively, in equity securities in a combination of Federal Reserve Bank and Federal Home Loan Bank stocks, which are restricted nonmarketable securities acquired to meet regulatory requirements. These securities are carried at cost.