
September 30, 2020	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses		Estimated Fair Value
Available-for-Sale:
U.S. Treasury notes	$	8.0	$	—	$	—	$	8.0
State, county and municipal securities	233.6		2.7		(0.2)		236.1
Obligations of U.S. government agencies	278.4		1.0		(0.6)		278.8
U.S. agency residential mortgage-backed securities & collateralized mortgage obligations	2,535.3		76.9		(0.5)		2,611.7
Private mortgage-backed securities	20.0		0.2		(0.1)		20.1
Corporate securities	292.9		5.4		(0.5)		297.8
Other investments	1.0		—		—		1.0
Total	$	3,369.2	$	86.2	$	(1.9)	$	3,453.5


September 30, 2020	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses		Estimated Fair Value
Held-to-Maturity:
State, county and municipal securities	$	49.9	$	3.2	$	—	$	53.1

U.S agency residential mortgage-backed securities & collateralized mortgage obligations	1.0		0.1		—		1.1
Corporate securities	4.0		0.1		—		4.1
Other investments	0.1		—		—		0.1
Total	$	55.0	$	3.4	$	—	$	58.4


December 31, 2019	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses		Estimated Fair Value
Available-for-Sale:
U.S. Treasury notes	$	9.0	$	—	$	—	$	9.0
State, county and municipal securities	80.1		0.8		—		80.9
Obligations of U.S. government agencies	367.5		0.1		(0.8)		366.8
U.S. agency residential mortgage-backed securities & collateralized mortgage obligations	2,303.6		19.6		(6.0)		2,317.2
Private mortgage-backed securities	47.6		—		(0.4)		47.2
Corporate securities	134.5		1.2		—		135.7
Other investments	3.2		—		—		3.2
Total	$	2,945.5	$	21.7	$	(7.2)	$	2,960.0


December 31, 2019	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses		Estimated Fair Value
Held-to-Maturity:
State, county and municipal securities	$	57.3	$	2.1	$	—	$	59.4
Obligations of U.S. government agencies	19.8		—		—		19.8
U.S. agency residential mortgage-backed securities & collateralized mortgage obligations	1.2		—		—		1.2
Corporate securities	13.9		0.1		—		14.0
Other investments	0.1		—		—		0.1
Total	$	92.3	$	2.2	$	—	$	94.5

There were no material gross realized gains or losses from the disposition of available-for-sale investment securities for the three and nine month periods ended September 30, 2020 and 2019.

As of September 30, 2020, the Company had general obligation securities with amortized costs of $41.9 million included in state, county and municipal securities, of which $27.8 million, or 66.3%, 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 available-for-sale investment securities, aggregated by investment category, and the length of time individual investment securities have been in a continuous unrealized loss position as of September 30, 2020 and December 31, 2019. There was no material allowance for credit loss as of September 30, 2020.


	Less than 12 Months				12 Months or More				Total
September 30, 2020	Fair Value		Gross Unrealized Losses		Fair Value		Gross Unrealized Losses		Fair Value		Gross Unrealized Losses
Available-for-Sale:

State, county and municipal securities	$	22.6	$	(0.2)	$	—	$	—	$	22.6	$	(0.2)
Obligations of U.S. government agencies	102.0		(0.6)		—		—		102.0		(0.6)
U.S. agency residential mortgage-backed securities & collateralized mortgage obligations	88.2		(0.4)		11.4		(0.1)		99.6		(0.5)
Private mortgage-backed securities	—		—		12.7		(0.1)		12.7		(0.1)
Corporate securities	54.1		(0.5)		—		—		54.1		(0.5)

Total	$	266.9	$	(1.7)	$	24.1	$	(0.2)	$	291.0	$	(1.9)


	Less than 12 Months				12 Months or More				Total
December 31, 2019	Fair Value		Gross Unrealized Losses		Fair Value		Gross Unrealized Losses		Fair Value		Gross Unrealized Losses
Available-for-Sale:

Obligations of U.S. government agencies	$	185.3	$	(0.8)	$	—	$	—	$	185.3	$	(0.8)
U.S. agency residential mortgage-backed securities & collateralized mortgage obligations	740.1		(4.6)		155.9		(1.4)		896.0		(6.0)
Private mortgage-backed securities	—		—		46.6		(0.4)		46.6		(0.4)


Total	$	925.4	$	(5.4)	$	202.5	$	(1.8)	$	1,127.9	$	(7.2)

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 127 and 331 individual available-for-sale investment securities that were in an unrealized loss position as of September 30, 2020 and December 31, 2019, respectively, related primarily to fluctuations in current interest rates. As of September 30, 2020, 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 was not a material allowance for credit losses during the three and nine month periods ended September 30, 2020 or 2019 for available-for-sale or held-to-maturity securities.

Maturities of investment securities at September 30, 2020 are shown 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
September 30, 2020	Amortized Cost		Estimated Fair Value		Amortized Cost		Estimated Fair Value
Within one year	$	652.4	$	931.3	$	8.9	$	8.9
After one year but within five years	1,446.5		1,251.2		30.5		31.9
After five years but within ten years	627.9		864.5		14.1		16.1
After ten years	642.4		406.5		1.5		1.5
Total	$	3,369.2	$	3,453.5	$	55.0	$	58.4

As of September 30, 2020, the Company held investment securities callable within one year with amortized costs and estimated fair values of $252.5 million and $252.5 million, respectively. These investment securities are primarily included in the “after one year but within five years” category in the table above. As of September 30, 2020, the Company held no callable structured notes.

As of September 30, 2020 and December 31, 2019, the Company recorded amortized costs of $2,097.6 million and $2,132.0 million, respectively, for investment securities. These investment securities were pledged to secure public deposits and securities sold under repurchase agreements and had an approximate fair value at September 30, 2020 and December 31, 2019 of $2,165.0 million and $2,144.9 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.