
March 31, 2021	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses		Estimated Fair Value
Available-for-Sale:
U.S. Treasury notes	$	1.0	$	—	$	—	$	1.0
State, county, and municipal securities	458.0		1.8		(14.7)		445.1
Obligations of U.S. government agencies	334.9		0.4		(11.8)		323.5
U.S. agency residential mortgage-backed securities & collateralized mortgage obligations	2,866.0		56.3		(20.8)		2,901.5
Private mortgage-backed securities	6.5		0.1		—		6.6

Corporate securities	344.6		3.7		(5.9)		342.4

Total	$	4,011.0	$	62.3	$	(53.2)	$	4,020.1


March 31, 2021	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses		Estimated Fair Value
Held-to-Maturity:
State, county, and municipal securities	$	74.1	$	2.7	$	(0.9)	$	75.9

U.S agency residential mortgage-backed securities & collateralized mortgage obligations	788.2		0.2		(12.8)		775.6
Corporate securities	3.9		0.1		—		4.0
Other investments	0.1		—		—		0.1
Total	$	866.3	$	3.0	$	(13.7)	$	855.6


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

There were no material gross realized gains and no material gross losses on the disposition of available-for-sale investment securities during the three month periods ended March 31, 2021 and 2020.

As of March 31, 2021, the Company had general obligation securities with amortized costs of $60.9 million included in state, county, and municipal securities, of which $25.6 million, or 42.0%, 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 a continuous unrealized loss position as of March 31, 2021 and December 31, 2020. There were no held-to-maturity securities in a continuous unrealized loss position at December 31, 2020.


	Less than 12 Months				12 Months or More				Total
March 31, 2021	Fair Value		Gross Unrealized Losses		Fair Value		Gross Unrealized Losses		Fair Value		Gross Unrealized Losses
Available-for-Sale:

State, county, and municipal securities	$	444.8	$	(14.7)	$	—	$	—	$	444.8	$	(14.7)
Obligations of U.S. government agencies	323.6		(11.8)		—		—		323.6		(11.8)
U.S. agency residential mortgage-backed securities & collateralized mortgage obligations	2,750.0		(20.7)		11.3		(0.1)		2,761.3		(20.8)

Corporate securities	342.3		(5.9)		—		—		342.3		(5.9)

Total	$	3,860.7	$	(53.1)	$	11.3	$	(0.1)	$	3,872.0	$	(53.2)




	Less than 12 Months				12 Months or More				Total
March 31, 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	$	775.6	$	(12.8)	$	—	$	—	$	775.6	$	(12.8)
State, county, and municipal securities	75.9		(0.9)		—		—		75.9		(0.9)
Total	$	851.5	$	(13.7)	$	—	$	—	$	851.5	$	(13.7)


	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.

The Company had 292 and 181 individual available-for-sale investment securities that were in an unrealized loss position as of March 31, 2021 and December 31, 2020, respectively, related primarily to fluctuations in current interest rates. As of March 31, 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 have the intent to sell any of the available-for-sale securities in the above table and it is more likely than not that the Company will not have to sell any securities before a recovery in cost. There were no material allowances for credit loss as of March 31, 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. As of March 31, 2021, the Company had variable rate mortgage-backed securities with an amortized cost of $235.8 million classified as available-for-sale in the table below. 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
March 31, 2021	Amortized Cost		Estimated Fair Value		Amortized Cost		Estimated Fair Value
Within one year	$	977.9	$	948.3	$	341.0	$	335.7
After one year but within five years	1,124.4		1,335.7		195.6		194.0
After five years but within ten years	1,062.5		1,038.5		147.5		146.9
After ten years	846.2		697.6		182.2		179.0
Total	$	4,011.0	$	4,020.1	$	866.3	$	855.6

As of March 31, 2021, the Company held investment securities callable within one year with amortized costs and estimated fair values of $265.1 million and $258.6 million, respectively. These investment securities are primarily included in the “after five years but within ten years” category in the table above. As of March 31, 2021, the Company held no callable structured notes.

As of March 31, 2021 and December 31, 2020, the Company recorded amortized costs of $2,257.0 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 March 31, 2021 and December 31, 2020 of $2,290.8 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.