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Investment Securities
12 Months Ended
Dec. 31, 2021
Investments, Debt and Equity Securities [Abstract]  
Investment Securities INVESTMENT SECURITIES
The amortized cost and approximate fair values of investment securities are summarized as follows:
December 31, 2021Amortized
Cost
Gross
Unrealized
Gains
Gross
Unrealized
Losses
Estimated
Fair
Value
Available-for-Sale
U.S. Treasury notes$697.6 $— $(12.9)$684.7 
State, county, and municipal securities434.7 2.1 (9.3)427.5 
Obligations of U.S. government agencies356.0 0.1 (9.2)346.9 
U.S. agency residential & commercial mortgage-backed securities & collateralized mortgage obligations2,027.3 14.1 (23.3)2,018.1 
Private mortgage-backed securities174.4 0.1 (1.1)173.4 
Collateralized loan obligations898.2 1.2 — 899.4 
Corporate Securities271.1 3.0 (3.6)270.5 
Total$4,859.3 $20.6 $(59.4)$4,820.5 

December 31, 2021Amortized
Cost
Gross
Unrealized
Gains
Gross
Unrealized
Losses
Estimated
Fair
Value
Held-to Maturity
State, county, and municipal securities$67.6 $2.0 $(0.4)$69.2 
U.S agency residential & commercial mortgage-backed securities & collateralized mortgage obligations (1)
1,609.0 13.2 (35.3)1,586.9 
Corporate securities11.0 0.4 — 11.4 
Total$1,687.6 $15.6 $(35.7)$1,667.5 
(1) Amortized costs presented above include $20.1 million of unamortized gains in U.S. agency residential and commercial mortgage-backed securities and collateralized mortgage obligations related to the 2021 second quarter transfer of securities from available-for-sale to held-to-maturity.
December 31, 2020Amortized
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 agencies332.9 1.0 (2.0)331.9 
U.S. agency residential & commercial mortgage-backed securities & collateralized mortgage obligations2,830.8 69.3 (2.5)2,897.6 
Private mortgage-backed securities10.9 0.1 (0.1)10.9 
Corporate Securities295.8 6.5 (0.1)302.2 
Other investments0.2 — — 0.2 
Total$3,932.7 $81.7 $(5.7)$4,008.7 
December 31, 2020Amortized
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 & commercial mortgage-backed securities & collateralized mortgage obligations1.0 0.1 — 1.1 
Corporate securities3.9 0.1 — 4.0 
Other investments0.1 — — 0.1 
Total$51.6 $3.4 $— $55.0 
There were $3.2 million in gross realized gains and $2.1 million in gross realized losses on the disposition of available-for-sale securities during 2021, with no material gross realized gains and no material gross realized losses on the disposition of available-for-sale securities during 2020, or 2019.
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 and commercial 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.
As of December 31, 2021, the Company had general obligation securities with amortized costs of $55.9 million included in state, county, and municipal securities, of which $40.7 million, or 72.8% 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 December 31, 2021 and 2020. There were no held-to-maturity securities in a continuous unrealized loss position as of December 31, 2020.
 Less than 12 Months12 Months or MoreTotal
December 31, 2021Fair
Value
Gross
Unrealized
Losses
Fair
Value
Gross
Unrealized
Losses
Fair
Value
Gross
Unrealized
Losses
Available-for-Sale      
U.S. Treasury notes$684.7 $(12.9)$— $— $684.7 $(12.9)
State, county, and municipal securities278.7 (9.1)5.0 (0.2)283.7 (9.3)
Obligations of U.S. government agencies297.0 (8.9)16.4 (0.3)313.4 (9.2)
U.S. agency residential & commercial mortgage-backed securities & collateralized mortgage obligations1,262.8 (23.0)26.4 (0.3)1,289.2 (23.3)
Private mortgage-backed securities127.2 (1.1)— — 127.2 (1.1)
Corporate securities109.9 (3.3)20.9 (0.3)130.8 (3.6)
Total$2,760.3 $(58.3)$68.7 $(1.1)$2,829.0 $(59.4)
 Less than 12 Months12 Months or MoreTotal
December 31, 2021Fair
Value
Gross
Unrealized
Losses
Fair
Value
Gross
Unrealized
Losses
Fair
Value
Gross
Unrealized
Losses
Held-to-Maturity      
U.S. agency residential & commercial mortgage-backed securities & collateralized mortgage obligations1,038.7 (35.3)— — 1,038.7 (35.3)
State, county and municipal securities29.0 (0.4)— — 29.0 (0.4)
Total$1,067.7 $(35.7)$— $— $1,067.7 $(35.7)
 Less than 12 Months12 Months or MoreTotal
December 31, 2020Fair
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 & commercial mortgage-backed securities & collateralized mortgage obligations434.0 (2.4)12.3 (0.1)446.3 (2.5)
Private mortgage-backed securities— — 4.3 (0.1)4.3 (0.1)
Corporate securities20.9 (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 285 and 181 individual investment securities as of December 31, 2021 and 2020, respectively, that were in an unrealized loss position, related primarily to fluctuations in the current interest rates. As of December 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 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 December 31, 2021 or 2020 and no impairment losses were recorded during 2019 for investment 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 securities and corporate securities which had an amortized costs of $84.8 million and $220.7 million, as of December 31, 2021 and 2020, respectively. 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-SaleHeld-to-Maturity
December 31, 2021Amortized
Cost
Estimated
Fair Value
Amortized
Cost
Estimated
Fair Value
Within one year$647.4 $742.8 $696.4 $687.2 
After one year but within five years1,482.4 1,577.4 374.5 363.6 
After five years but within ten years1,313.4 1,165.6 275.6 276.2 
After ten years1,416.1 1,334.7 341.1 340.5 
Total$4,859.3 $4,820.5 $1,687.6 $1,667.5 
As of December 31, 2021, the Company held investment securities callable within one year with amortized costs and estimated fair values of $236.1 million and $235.7 million, respectively. These investment securities are primarily classified as available-for-sale and included in the “after ten years category” in the table above. As of December 31, 2021, the Company had no callable structured notes.
There were no significant concentrations of investments at December 31, 2021, (greater than 10 percent of stockholders’ equity) in any individual security issuer, except for U.S. government or agency-backed securities.
As of December 31, 2021 and 2020, the Company recorded amortized costs of $2,617.8 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 December 31, 2021 and 2020 of $2,610.8 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.