Investment Securities

6 Months Ended

Jun. 30, 2021

Investments, Debt and Equity Securities [Abstract]

The amortized cost and the approximate fair values of investment securities are summarized as follows:


June 30, 2021	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses		Estimated Fair Value
Available-for-Sale:
U.S. Treasury notes	$	497.1	$	—	$	(0.2)	$	496.9
State, county, and municipal securities	449.2		2.5		(7.2)		444.5
Obligations of U.S. government agencies	333.2		0.4		(6.7)		326.9
U.S. agency residential mortgage-backed securities & collateralized mortgage obligations	2,064.7		29.4		(11.9)		2,082.2
Private mortgage-backed securities	16.9		0.1		—		17.0
Collateralized loan obligations	187.3		—		—		187.3
Corporate securities	401.0		4.6		(2.6)		403.0

Total	$	3,949.4	$	37.0	$	(28.6)	$	3,957.8


June 30, 2021	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses		Estimated Fair Value
Held-to-Maturity:
State, county, and municipal securities	$	72.4	$	2.6	$	(0.5)	$	74.5

U.S. agency residential mortgage-backed securities & collateralized mortgage obligations (1)	1,591.5		22.4		(8.6)		1,605.3
Corporate securities (1)	21.6		0.5		—		22.1

Total	$	1,685.5	$	25.5	$	(9.1)	$	1,701.9
(1) Amortized costs presented above include $24.4 million and $0.4 million of unamortized gains in U.S. agency residential mortgage-backed securities and collateralized mortgage obligations and Corporate securities, respectively, related to the 2021 second quarter transfer of securities from available-for-sale to held-to-maturity.


December 31, 2020	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses		Estimated Fair Value
Available-for-Sale:

State, county, and municipal securities	$	462.1	$	4.8	$	(1.0)	$	465.9
Obligations of U.S. government agencies	332.9		1.0		(2.0)		331.9
U.S. agency residential mortgage-backed securities & collateralized mortgage obligations	2,830.8		69.3		(2.5)		2,897.6
Private mortgage-backed securities	10.9		0.1		(0.1)		10.9
Corporate securities	295.8		6.5		(0.1)		302.2
Other investments	0.2		—		—		0.2
Total	$	3,932.7	$	81.7	$	(5.7)	$	4,008.7


December 31, 2020	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses		Estimated Fair Value
Held-to-Maturity:
State, county, and municipal securities	$	46.6	$	3.2	$	—	$	49.8

U.S. agency residential mortgage-backed securities & collateralized mortgage obligations	1.0		0.1		—		1.1
Corporate securities	3.9		0.1		—		4.0
Other investments	0.1		—		—		0.1
Total	$	51.6	$	3.4	$	—	$	55.0

On June 7, 2021, the Company transferred debt securities with an amortized cost of $646.7 million and an estimated fair value of $672.2 million from the available-for-sale to the held-to-maturity classification. These securities consisted of residential mortgage-backed securities and collateralized mortgage obligations ($629.4 million amortized cost and $654.5 million estimated fair value) and corporate securities ($17.3 million amortized cost and $17.7 million estimated fair value) and were transferred as the Company has the positive intent and ability to hold these securities to maturity. The transfer of debt securities into the held-to-maturity category was recorded at fair value on the date of transfer. The net unrealized gains on the transfer date are included in accumulated other comprehensive income and are being accreted over the remaining lives of the securities. This accretion is expected to offset the amortization of the related premium created by the investment securities transfer into the held-to-maturity classification, with no expected impact on future net income.

There were no material gross realized gains and no material gross losses on the disposition of available-for-sale investment securities during the three and six month periods ended June 30, 2021 and 2020.

As of June 30, 2021, the Company had general obligation securities with amortized costs of $59.1 million included in state, county, and municipal securities, of which $41.6 million, or 70.4%, were issued by political subdivisions or agencies within the states of Idaho, Montana, Oregon, South Dakota, Washington, and Wyoming.

The following tables show the gross unrealized losses and fair values of investment securities, aggregated by investment category, and the length of time individual investment securities have been in an unrealized loss position as of June 30, 2021 and December 31, 2020. There were no held-to-maturity securities in an unrealized loss position at December 31, 2020.


	Less than 12 Months				12 Months or More				Total
June 30, 2021	Fair Value		Gross Unrealized Losses		Fair Value		Gross Unrealized Losses		Fair Value		Gross Unrealized Losses
Available-for-Sale:
U.S. Treasury notes	$	496.9	$	(0.2)	$	—	$	—	$	496.9	$	(0.2)
State, county, and municipal securities	260.3		(7.2)		—		—		260.3		(7.2)
Obligations of U.S. government agencies	293.7		(6.7)		—		—		293.7		(6.7)
U.S. agency residential mortgage-backed securities & collateralized mortgage obligations	870.9		(11.9)		—		—		870.9		(11.9)

Corporate securities	196.2		(2.6)		—		—		196.2		(2.6)

Total	$	2,118.0	$	(28.6)	$	—	$	—	$	2,118.0	$	(28.6)




	Less than 12 Months				12 Months or More				Total
June 30, 2021	Fair Value		Gross Unrealized Losses		Fair Value		Gross Unrealized Losses		Fair Value		Gross Unrealized Losses
Held-to-Maturity:


U.S. agency residential mortgage-backed securities & collateralized mortgage obligations	$	742.0	$	(8.6)	$	—	$	—	$	742.0	$	(8.6)
State, county, and municipal securities	29.3		(0.5)		—		—		29.3		(0.5)
Total	$	771.3	$	(9.1)	$	—	$	—	$	771.3	$	(9.1)


	Less than 12 Months				12 Months or More				Total
December 31, 2020	Fair Value		Gross Unrealized Losses		Fair Value		Gross Unrealized Losses		Fair Value		Gross Unrealized Losses
Available-for-Sale:

State, county, and municipal securities	$	148.1	$	(1.0)	$	—	$	—	$	148.1	$	(1.0)
Obligations of U.S. government agencies	235.6		(2.0)		—		—		235.6		(2.0)
U.S. agency residential mortgage-backed securities & collateralized mortgage obligations	434.0		(2.4)		12.3		(0.1)		446.3		(2.5)
Private mortgage-backed securities	—		—		4.3		(0.1)		4.3		(0.1)
Corporate securities	20.9		(0.1)		—		—		20.9		(0.1)

Total	$	838.6	$	(5.5)	$	16.6	$	(0.2)	$	855.2	$	(5.7)

The available-for-sale securities portfolio 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. The unrealized losses are due to changes in interest rates and other market conditions.

As of June 30, 2021 and December 31, 2020, the Company had 260 and 181 individual investment securities, respectively, that were in an unrealized loss position, related primarily to fluctuations in current interest rates. As of June 30, 2021, the Company had the intent and ability to hold these investment securities for a period of time sufficient to allow for an anticipated recovery. Furthermore, 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. There were no material allowances for credit loss as of June 30, 2021 or December 31, 2020 for available-for-sale or held-to-maturity securities.

Maturities of securities do not reflect rate repricing opportunities present in adjustable-rate mortgage-backed securities. In the table below, the Company had variable rate mortgage-backed and corporate securities which had an amortized cost of $291.6 million and were classified as available-for-sale as of June 30, 2021. 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
June 30, 2021	Amortized Cost		Estimated Fair Value		Amortized Cost		Estimated Fair Value
Within one year	$	624.8	$	723.9	$	682.2	$	688.1
After one year but within five years	1,516.3		1,626.9		393.3		398.2
After five years but within ten years	1,062.4		935.5		272.9		276.0
After ten years	745.9		671.5		337.1		339.6
Total	$	3,949.4	$	3,957.8	$	1,685.5	$	1,701.9

As of June 30, 2021, the Company held investment securities callable within one year with amortized costs and estimated fair values of $151.2 million and $149.1 million, respectively. These investment securities are primarily included in the “after five years but within ten years” category in the table above. As of June 30, 2021, the Company held no callable structured notes.

As of June 30, 2021 and December 31, 2020, the Company recorded amortized costs of $2,425.7 million and $2,323.0 million, respectively, for investment securities pledged to secure public deposits and securities sold under repurchase agreements and had approximate fair values as of June 30, 2021 and December 31, 2020 of $2,456.0 million and $2,383.6 million, 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.