ORGANIZATION, CONSOLIDATION AND BASIS OF PRESENTATION Significant Accounting Policies (Policies)	9 Months Ended
Sep. 30, 2020
Credit Loss, Financial Instrument [Abstract]
ORGANIZATION, CONSOLIDATION, AND PRESENTATION OF FINANCIAL STATEMENTS	SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES Basis of presentation. The Consolidated Financial Statements of First Financial Bancorp., a financial holding company principally serving Ohio, Indiana, Kentucky and Illinois, include the accounts and operations of First Financial and its wholly-owned subsidiary, First Financial Bank. All significant intercompany transactions and accounts have been eliminated in consolidation. Certain reclassifications of prior periods' amounts have been made to conform to current year presentation. Such reclassifications had no effect on net earnings. These interim financial statements have been prepared in accordance with the instructions to Form 10-Q and Article 10 of Regulation S-X. Accordingly, they may not include all of the information and accompanying notes necessary to constitute a complete set of financial statements required by GAAP and should be read in conjunction with the audited consolidated financial statements and related notes included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2019. Management believes these unaudited consolidated financial statements reflect all adjustments of a normal recurring nature which are necessary for a fair presentation of the results for the interim periods presented. The results of operations for the interim periods are not necessarily indicative of the results that may be expected for the full year or any other interim period. The Consolidated Balance Sheet as of December 31, 2019 has been derived from the audited financial statements in the Company’s 2019 Form 10-K. Use of estimates. The preparation of financial statements in conformity with GAAP requires management to make estimates, assumptions and judgments that affect the amounts reported in the Consolidated Financial Statements and accompanying Notes. These estimates, assumptions and judgments are inherently subjective and may be susceptible to significant change. Actual realized amounts could differ materially from these estimates. COVID-19. In the first nine months of 2020, First Financial's operations and financial results were significantly impacted by the COVID-19 pandemic. The spread of COVID-19 has caused significant economic disruption throughout the United States as state and local governments issued stay at home orders and temporarily closed non-essential businesses. The potential financial impact from the pandemic is unknown at this time, however prolonged disruption may adversely impact several industries within the Company's geographic footprint and impair the ability of First Financial's customers to fulfill their contractual obligations to the Company. This could cause First Financial to experience a material adverse effect on business operations, asset valuations, financial condition and results of operations. Material adverse impacts may include all or a combination of valuation impairments on First Financial's intangible assets, investments, loans, mortgage servicing rights or counter-party risk derivatives. Investment securities. First Financial classifies debt securities into three categories: HTM, trading and AFS. Management classifies investment securities into the appropriate category at the time of purchase and re-evaluates that classification as deemed appropriate. Investment securities are classified as HTM when First Financial has the positive intent and ability to hold the securities to maturity. HTM securities are recorded at amortized cost. Investment securities classified as trading are held principally for resale in the near-term and are recorded at fair value. Fair value is determined using quoted market prices. Gains or losses on trading securities, both realized and unrealized, are reported in noninterest income. Investment securities not classified as either HTM or trading are classified as AFS. AFS securities are recorded at fair value, with the unrealized gains and losses, net of tax, reported as a separate component of accumulated other comprehensive income (loss) in shareholders' equity. The amortized cost of investment securities classified as either HTM or AFS is adjusted for amortization of premiums and accretion of discounts to maturity, or in the case of mortgage-backed securities, over the estimated life of the security. Such amortization and accretion are considered an adjustment to the yield on the security and included in interest income from investments. Interest and dividends are also included in interest income from investment securities in the Consolidated Statements of Income. Realized gains and losses are based on the amortized cost of the security sold using the specific identification method. Allowance for credit losses - held-to-maturity securities. Management measures expected credit losses on held-to-maturity debt securities on a collective basis by security type. The estimate of expected credit losses considers historical credit loss information that is adjusted for current conditions and reasonable and supportable forecasts. Management classifies the held-to-maturity portfolio into the following major security types: Mortgage-backed, CMOs and Obligations of state and other political subdivisions. Nearly all of the HTM securities held by the Company are issued by U.S. government entities and agencies. These securities are either explicitly or implicitly guaranteed by the U.S. government, are highly rated by major rating agencies and have a long history of no credit losses. The remainder of the Company's HTM securities are non-agency collateralized mortgage obligations and obligations of state and other political subdivisions which currently carry ratings no lower than A+. Accrued interest receivable on held-to maturity debt securities, which totaled $0.2 million as of September 30, 2020, is excluded by policy election from the estimate of credit losses. Allowance for credit losses - available-for-sale securities. For available-for-sale debt securities in an unrealized loss position, the Company first assesses whether it intends to sell, or it is more likely than not that it will be required to sell the security before recovery of its amortized cost basis. If either of the criteria regarding intent or requirement to sell is met, the security’s amortized cost basis is written down to fair value through income. For debt securities available-for-sale that do not meet the aforementioned criteria, the Company evaluates whether the decline in fair value has resulted from credit losses or other factors. In making this assessment, management considers the extent to which fair value is less than amortized cost, any changes to the rating of the security by a rating agency and adverse conditions specifically related to the security, among other factors. If this assessment indicates that a credit loss exists, the present value of cash flows expected to be collected from the security are compared to the amortized cost basis of the security. If the present value of cash flows expected to be collected is less than the amortized cost basis, a credit loss exists and an allowance for credit losses is recorded, limited by the amount that the fair value is less than the amortized cost basis. Any impairment that has not been recorded through an allowance for credit loss is recognized in other comprehensive income. Changes in the allowance for credit losses are recorded as provision for credit loss expense. Losses are charged against the allowance when management believes the uncollectibility of an available-for-sale security is confirmed or when either of the criteria regarding intent or requirement to sell is met. Accrued interest receivable on available-for-sale debt securities, which totaled $11.7 million as of September 30, 2020, is excluded from the estimate of credit losses. Allowance for credit losses - loans and leases. The allowance for credit losses is a valuation account that is deducted from the loans’ amortized cost basis to present the net amount expected to be collected on the loans. Management's determination of the adequacy of the ACL is based on an assessment of the expected credit losses on loan and leases over the expected life of the loan. The ACL is increased by provision expense and decreased by charge-offs, net of recoveries of amounts previously charged-off. Loans are charged off when management believes that the collection of the principal amount owed in full, either through payments from the borrower or a guarantor or from the liquidation of collateral, is unlikely. Expected recoveries do not exceed the aggregate of amounts previously charged-off and expected to be charged-off. Any interest that is accrued but not collected is reversed against interest income when a loan is placed on nonaccrual status, which typically occurs prior to charging off all, or a portion, of a loan. The Company made the policy election to exclude accrued interest receivable on loans and leases from the estimate of credit losses. Management estimates the allowance balance using relevant available information from both internal and external sources, relating to past events, current conditions and reasonable and supportable forecasts. Historical credit loss experience paired with economic forecasts provide the basis for the quantitatively modeled estimation of expected credit losses. First Financial adjusts its quantitative model, as necessary, to reflect conditions not already considered by the quantitative model. These adjustments are commonly known as the Qualitative Framework. First Financial quantitatively models expected credit loss using PD, LGD and EAD over the R&S forecast period, reversion and post-reversion periods. Utilizing third-party software, the Bank forecasts PD by using a parameterized transition matrix approach. Average transition matrices are calculated over the TTC period, which was defined as the period from December 2007 to December 2016. TTC transition matrices are adjusted under forward-looking macroeconomic expectations to obtain R&S forecasts. First Financial is not required to develop forecasts over full the contractual term of the financial asset or group of financial assets. Rather, for periods beyond which the entity is able to make or obtain R&S forecasts of expected credit losses, the Company reverts in a straight line manner over a one year period to an average TTC loss level that is reflective of the prepayment adjusted contractual term of the financial asset or group of financial assets. The R&S period, elected by the bank to be two years, is forecasted using econometric data sourced from Moody's, an industry-leading independent third party. FFB utilizes a non-parametric loss curve approach embedded within a third-party software for estimating LGD. The PD multiplied by LGD produces an expected loss rate that, when calculating the ACL, is applied to contractual loan cash flows, adjusted for expected future rates of principal prepayments. The Company adjusts its quantitative model for certain qualitative factors to reflect the extent to which management expects current conditions and R&S forecasts to differ from the conditions that existed for the period over which historical information was evaluated. The Qualitative Framework reflects changes related to relevant data, such as changes in asset quality trends, portfolio growth and composition, national and local economic factors, credit policy and administration and other factors not considered in the base quantitative model. Loans that do not share risk characteristics are evaluated on an individual basis. First Financial will typically evaluate on an individual basis any loans that are on nonaccrual, designated as a TDR, or reasonably expected to be designated as a TDR. When management determines that foreclosure is probable or when repayment is expected to be provided substantially through the operation or sale of underlying collateral, expected credit losses are based on the fair value of the collateral at the reporting date, adjusted for selling costs. For loans evaluated on an individual basis that are not determined to be collateral dependent, a discounted cash flow analysis is performed to determine expected credit losses. Expected credit losses are estimated over the contractual term of the loans, adjusted for expected prepayments when appropriate. The contractual term excludes expected extensions, renewals and modifications unless either of the following applies: management has a reasonable expectation at the reporting date that a troubled debt restructuring will be executed with an individual borrower or the extension or renewal options are included in the original or modified contract at the reporting date and are not unconditionally cancellable by the Company. Credit card receivables do not have stated maturities. In determining the estimated life of a credit card receivable, management first estimates the future cash flows expected to be received and then applies those expected future cash flows to the credit card balance. Allowance for credit losses - unfunded commitments. Effective January 1, 2020, First Financial adopted ASC 326, at which time First Financial estimated expected credit losses over the contractual period in which the Company is exposed to credit risk via a contractual obligation to extend credit, unless that obligation is unconditionally cancellable by the Company. The estimate includes consideration of the likelihood that funding will occur and an estimate of expected credit losses on commitments expected to be funded over its estimated life consistent with the Company's ACL methodology for loans and leases. Adjustments to the reserve for unfunded commitments are recorded in Provision for credit losses - unfunded commitments in the Consolidated Statements of Income. Prior to the adoption of ASC 326, First Financial maintained its reserve to absorb probable losses incurred in standby letters of credit and outstanding loan commitments. First Financial determined the adequacy of this reserve based upon an evaluation of the unfunded credit facilities, which included consideration of historical commitment utilization experience, credit risk ratings and historical loss rates, consistent with the Company's ALLL methodology at the time.
Basis of Presentation Policy	Basis of presentation. The Consolidated Financial Statements of First Financial Bancorp., a financial holding company principally serving Ohio, Indiana, Kentucky and Illinois, include the accounts and operations of First Financial and its wholly-owned subsidiary, First Financial Bank. All significant intercompany transactions and accounts have been eliminated in consolidation. Certain reclassifications of prior periods' amounts have been made to conform to current year presentation. Such reclassifications had no effect on net earnings. These interim financial statements have been prepared in accordance with the instructions to Form 10-Q and Article 10 of Regulation S-X. Accordingly, they may not include all of the information and accompanying notes necessary to constitute a complete set of financial statements required by GAAP and should be read in conjunction with the audited consolidated financial statements and related notes included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2019. Management believes these unaudited consolidated financial statements reflect all adjustments of a normal recurring nature which are necessary for a fair presentation of the results for the interim periods presented. The results of operations for the interim periods are not necessarily indicative of the results that may be expected for the full year or any other interim period. The Consolidated Balance Sheet as of December 31, 2019 has been derived from the audited financial statements in the Company’s 2019 Form 10-K.
Use of Estimates, Policy	Use of estimates. The preparation of financial statements in conformity with GAAP requires management to make estimates, assumptions and judgments that affect the amounts reported in the Consolidated Financial Statements and accompanying Notes. These estimates, assumptions and judgments are inherently subjective and may be susceptible to significant change. Actual realized amounts could differ materially from these estimates.
Investment, Policy [Policy Text Block]	Investment securities. First Financial classifies debt securities into three categories: HTM, trading and AFS. Management classifies investment securities into the appropriate category at the time of purchase and re-evaluates that classification as deemed appropriate. Investment securities are classified as HTM when First Financial has the positive intent and ability to hold the securities to maturity. HTM securities are recorded at amortized cost. Investment securities classified as trading are held principally for resale in the near-term and are recorded at fair value. Fair value is determined using quoted market prices. Gains or losses on trading securities, both realized and unrealized, are reported in noninterest income. Investment securities not classified as either HTM or trading are classified as AFS. AFS securities are recorded at fair value, with the unrealized gains and losses, net of tax, reported as a separate component of accumulated other comprehensive income (loss) in shareholders' equity. The amortized cost of investment securities classified as either HTM or AFS is adjusted for amortization of premiums and accretion of discounts to maturity, or in the case of mortgage-backed securities, over the estimated life of the security. Such amortization and accretion are considered an adjustment to the yield on the security and included in interest income from investments. Interest and dividends are also included in interest income from investment securities in the Consolidated Statements of Income. Realized gains and losses are based on the amortized cost of the security sold using the specific identification method.
Credit Loss, Financial Instrument [Policy Text Block]	Allowance for credit losses - held-to-maturity securities. Management measures expected credit losses on held-to-maturity debt securities on a collective basis by security type. The estimate of expected credit losses considers historical credit loss information that is adjusted for current conditions and reasonable and supportable forecasts. Management classifies the held-to-maturity portfolio into the following major security types: Mortgage-backed, CMOs and Obligations of state and other political subdivisions. Nearly all of the HTM securities held by the Company are issued by U.S. government entities and agencies. These securities are either explicitly or implicitly guaranteed by the U.S. government, are highly rated by major rating agencies and have a long history of no credit losses. The remainder of the Company's HTM securities are non-agency collateralized mortgage obligations and obligations of state and other political subdivisions which currently carry ratings no lower than A+. Accrued interest receivable on held-to maturity debt securities, which totaled $0.2 million as of September 30, 2020, is excluded by policy election from the estimate of credit losses. Allowance for credit losses - available-for-sale securities. For available-for-sale debt securities in an unrealized loss position, the Company first assesses whether it intends to sell, or it is more likely than not that it will be required to sell the security before recovery of its amortized cost basis. If either of the criteria regarding intent or requirement to sell is met, the security’s amortized cost basis is written down to fair value through income. For debt securities available-for-sale that do not meet the aforementioned criteria, the Company evaluates whether the decline in fair value has resulted from credit losses or other factors. In making this assessment, management considers the extent to which fair value is less than amortized cost, any changes to the rating of the security by a rating agency and adverse conditions specifically related to the security, among other factors. If this assessment indicates that a credit loss exists, the present value of cash flows expected to be collected from the security are compared to the amortized cost basis of the security. If the present value of cash flows expected to be collected is less than the amortized cost basis, a credit loss exists and an allowance for credit losses is recorded, limited by the amount that the fair value is less than the amortized cost basis. Any impairment that has not been recorded through an allowance for credit loss is recognized in other comprehensive income. Changes in the allowance for credit losses are recorded as provision for credit loss expense. Losses are charged against the allowance when management believes the uncollectibility of an available-for-sale security is confirmed or when either of the criteria regarding intent or requirement to sell is met. Accrued interest receivable on available-for-sale debt securities, which totaled $11.7 million as of September 30, 2020, is excluded from the estimate of credit losses.
Loans and Leases Receivable, Allowance for Loan Losses Policy	Allowance for credit losses - loans and leases. The allowance for credit losses is a valuation account that is deducted from the loans’ amortized cost basis to present the net amount expected to be collected on the loans. Management's determination of the adequacy of the ACL is based on an assessment of the expected credit losses on loan and leases over the expected life of the loan. The ACL is increased by provision expense and decreased by charge-offs, net of recoveries of amounts previously charged-off. Loans are charged off when management believes that the collection of the principal amount owed in full, either through payments from the borrower or a guarantor or from the liquidation of collateral, is unlikely. Expected recoveries do not exceed the aggregate of amounts previously charged-off and expected to be charged-off. Any interest that is accrued but not collected is reversed against interest income when a loan is placed on nonaccrual status, which typically occurs prior to charging off all, or a portion, of a loan. The Company made the policy election to exclude accrued interest receivable on loans and leases from the estimate of credit losses. Management estimates the allowance balance using relevant available information from both internal and external sources, relating to past events, current conditions and reasonable and supportable forecasts. Historical credit loss experience paired with economic forecasts provide the basis for the quantitatively modeled estimation of expected credit losses. First Financial adjusts its quantitative model, as necessary, to reflect conditions not already considered by the quantitative model. These adjustments are commonly known as the Qualitative Framework. First Financial quantitatively models expected credit loss using PD, LGD and EAD over the R&S forecast period, reversion and post-reversion periods. Utilizing third-party software, the Bank forecasts PD by using a parameterized transition matrix approach. Average transition matrices are calculated over the TTC period, which was defined as the period from December 2007 to December 2016. TTC transition matrices are adjusted under forward-looking macroeconomic expectations to obtain R&S forecasts. First Financial is not required to develop forecasts over full the contractual term of the financial asset or group of financial assets. Rather, for periods beyond which the entity is able to make or obtain R&S forecasts of expected credit losses, the Company reverts in a straight line manner over a one year period to an average TTC loss level that is reflective of the prepayment adjusted contractual term of the financial asset or group of financial assets. The R&S period, elected by the bank to be two years, is forecasted using econometric data sourced from Moody's, an industry-leading independent third party. FFB utilizes a non-parametric loss curve approach embedded within a third-party software for estimating LGD. The PD multiplied by LGD produces an expected loss rate that, when calculating the ACL, is applied to contractual loan cash flows, adjusted for expected future rates of principal prepayments. The Company adjusts its quantitative model for certain qualitative factors to reflect the extent to which management expects current conditions and R&S forecasts to differ from the conditions that existed for the period over which historical information was evaluated. The Qualitative Framework reflects changes related to relevant data, such as changes in asset quality trends, portfolio growth and composition, national and local economic factors, credit policy and administration and other factors not considered in the base quantitative model. Loans that do not share risk characteristics are evaluated on an individual basis. First Financial will typically evaluate on an individual basis any loans that are on nonaccrual, designated as a TDR, or reasonably expected to be designated as a TDR. When management determines that foreclosure is probable or when repayment is expected to be provided substantially through the operation or sale of underlying collateral, expected credit losses are based on the fair value of the collateral at the reporting date, adjusted for selling costs. For loans evaluated on an individual basis that are not determined to be collateral dependent, a discounted cash flow analysis is performed to determine expected credit losses. Expected credit losses are estimated over the contractual term of the loans, adjusted for expected prepayments when appropriate. The contractual term excludes expected extensions, renewals and modifications unless either of the following applies: management has a reasonable expectation at the reporting date that a troubled debt restructuring will be executed with an individual borrower or the extension or renewal options are included in the original or modified contract at the reporting date and are not unconditionally cancellable by the Company. Credit card receivables do not have stated maturities. In determining the estimated life of a credit card receivable, management first estimates the future cash flows expected to be received and then applies those expected future cash flows to the credit card balance.The allowance for credit losses is a valuation account that is deducted from the loans’ amortized cost basis to present the net amount expected to be collected on the loans. The ACL is increased by provision expense and decreased by charge-offs, net of recoveries of amounts previously charged-off. First Financial's policy is to charge-off all or a portion of a loan when, in management's opinion, it is unlikely to collect the principal amount owed in full either through payments from the borrower or a guarantor or from the liquidation of collateral. Expected recoveries do not exceed the aggregate of amounts previously charged-off and expected to be charged-off. Accrued interest receivable on loans and leases, which totaled $41.2 million as of September 30, 2020, is excluded from the estimate of credit losses. Management estimates the allowance balance using relevant available information from both internal and external sources, relating to past events, current conditions and reasonable and supportable forecasts. Historical credit loss experience paired with economic forecasts provides the basis for the quantitatively modeled estimation of expected credit losses. First Financial adjusts its quantitative model, as necessary, to reflect conditions not already considered by the quantitative model. These adjustments are commonly known as the Qualitative Framework. The allowance for credit losses is measured on a collective (pool) basis when similar risk characteristics exist.
Commitments and Contingencies, Policy	Allowance for credit losses - unfunded commitments. Effective January 1, 2020, First Financial adopted ASC 326, at which time First Financial estimated expected credit losses over the contractual period in which the Company is exposed to credit risk via a contractual obligation to extend credit, unless that obligation is unconditionally cancellable by the Company. The estimate includes consideration of the likelihood that funding will occur and an estimate of expected credit losses on commitments expected to be funded over its estimated life consistent with the Company's ACL methodology for loans and leases. Adjustments to the reserve for unfunded commitments are recorded in Provision for credit losses - unfunded commitments in the Consolidated Statements of Income.Prior to the adoption of ASC 326, First Financial maintained its reserve to absorb probable losses incurred in standby letters of credit and outstanding loan commitments. First Financial determined the adequacy of this reserve based upon an evaluation of the unfunded credit facilities, which included consideration of historical commitment utilization experience, credit risk ratings and historical loss rates, consistent with the Company's ALLL methodology at the time. First Financial offers a variety of financial instruments including loan commitments and letters of credit to assist clients in meeting their requirement for liquidity and credit enhancement. GAAP does not require these financial instruments to be recorded in the Consolidated Financial Statements. First Financial utilizes the same credit policies in issuing commitments and conditional obligations as it does for credit instruments recorded on the Consolidated Balance Sheets. First Financial’s exposure to credit loss in the event of non-performance by the counterparty was represented by the contractual amounts of those instruments. Effective January 1, 2020, First Financial adopted ASC 326, at which time First Financial estimated expected credit losses over the contractual period in which the Company is exposed to credit risk via a contractual obligation to extend credit, unless that obligation is unconditionally cancellable by the Company. The estimate includes consideration of the likelihood that funding will occur and an estimate of expected credit losses on commitments expected to be funded over its estimated life consistent with the Company's ACL methodology for loans and leases. Adjustments to the reserve for unfunded commitments are recorded in Provision for credit losses - unfunded commitments in the Consolidated Statements of Income. First Financial had $14.8 million of ACL for unfunded commitments recorded in Accrued interest and other liabilities on the Consolidated Balance Sheets as of September 30, 2020. Prior to the adoption of ASC 326, First Financial maintained its reserve to absorb probable losses incurred in standby letters of credit and outstanding loan commitments. First Financial determined the adequacy of this reserve based upon an evaluation of the unfunded credit facilities, which included consideration of historical commitment utilization experience, credit risk ratings and historical loss rates, consistent with the Company's ALLL methodology at the time.

ORGANIZATION, CONSOLIDATION AND BASIS OF PRESENTATION Significant Accounting Policies (Policies)

9 Months Ended

Sep. 30, 2020

Credit Loss, Financial Instrument [Abstract]

ORGANIZATION, CONSOLIDATION, AND PRESENTATION OF FINANCIAL STATEMENTS

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES

Basis of presentation. The Consolidated Financial Statements of First Financial Bancorp., a financial holding company principally serving Ohio, Indiana, Kentucky and Illinois, include the accounts and operations of First Financial and its wholly-owned subsidiary, First Financial Bank. All significant intercompany transactions and accounts have been eliminated in consolidation. Certain reclassifications of prior periods' amounts have been made to conform to current year presentation. Such reclassifications had no effect on net earnings.

These interim financial statements have been prepared in accordance with the instructions to Form 10-Q and Article 10 of Regulation S-X. Accordingly, they may not include all of the information and accompanying notes necessary to constitute a complete set of financial statements required by GAAP and should be read in conjunction with the audited consolidated financial statements and related notes included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2019. Management believes these unaudited consolidated financial statements reflect all adjustments of a normal recurring nature which are necessary for a fair presentation of the results for the interim periods presented. The results of operations for the interim periods are not necessarily indicative of the results that may be expected for the full year or any other interim period. The Consolidated Balance Sheet as of December 31, 2019 has been derived from the audited financial statements in the Company’s 2019 Form 10-K.

Use of estimates. The preparation of financial statements in conformity with GAAP requires management to make estimates, assumptions and judgments that affect the amounts reported in the Consolidated Financial Statements and accompanying Notes. These estimates, assumptions and judgments are inherently subjective and may be susceptible to significant change. Actual realized amounts could differ materially from these estimates.

COVID-19. In the first nine months of 2020, First Financial's operations and financial results were significantly impacted by the COVID-19 pandemic. The spread of COVID-19 has caused significant economic disruption throughout the United States as state and local governments issued stay at home orders and temporarily closed non-essential businesses. The potential financial impact from the pandemic is unknown at this time, however prolonged disruption may adversely impact several industries within the Company's geographic footprint and impair the ability of First Financial's customers to fulfill their contractual obligations to the Company. This could cause First Financial to experience a material adverse effect on business operations, asset valuations, financial condition and results of operations. Material adverse impacts may include all or a combination of valuation impairments on First Financial's intangible assets, investments, loans, mortgage servicing rights or counter-party risk derivatives.

Investment securities. First Financial classifies debt securities into three categories: HTM, trading and AFS. Management classifies investment securities into the appropriate category at the time of purchase and re-evaluates that classification as deemed appropriate.

Investment securities are classified as HTM when First Financial has the positive intent and ability to hold the securities to maturity. HTM securities are recorded at amortized cost.

Investment securities classified as trading are held principally for resale in the near-term and are recorded at fair value. Fair value is determined using quoted market prices. Gains or losses on trading securities, both realized and unrealized, are reported in noninterest income.

Investment securities not classified as either HTM or trading are classified as AFS. AFS securities are recorded at fair value, with the unrealized gains and losses, net of tax, reported as a separate component of accumulated other comprehensive income (loss) in shareholders' equity.

The amortized cost of investment securities classified as either HTM or AFS is adjusted for amortization of premiums and accretion of discounts to maturity, or in the case of mortgage-backed securities, over the estimated life of the security. Such amortization and accretion are considered an adjustment to the yield on the security and included in interest income from investments. Interest and dividends are also included in interest income from investment securities in the Consolidated Statements of Income. Realized gains and losses are based on the amortized cost of the security sold using the specific identification method.

Allowance for credit losses - held-to-maturity securities. Management measures expected credit losses on held-to-maturity debt securities on a collective basis by security type. The estimate of expected credit losses considers historical credit loss information that is adjusted for current conditions and reasonable and supportable forecasts. Management classifies the held-to-maturity portfolio into the following major security types: Mortgage-backed, CMOs and Obligations of state and other political subdivisions.

Nearly all of the HTM securities held by the Company are issued by U.S. government entities and agencies. These securities are either explicitly or implicitly guaranteed by the U.S. government, are highly rated by major rating agencies and have a long history of no credit losses. The remainder of the Company's HTM securities are non-agency collateralized mortgage obligations and obligations of state and other political subdivisions which currently carry ratings no lower than A+. Accrued interest receivable on held-to maturity debt securities, which totaled $0.2 million as of September 30, 2020, is excluded by policy election from the estimate of credit losses.

Allowance for credit losses - available-for-sale securities. For available-for-sale debt securities in an unrealized loss position, the Company first assesses whether it intends to sell, or it is more likely than not that it will be required to sell the security before recovery of its amortized cost basis. If either of the criteria regarding intent or requirement to sell is met, the security’s amortized cost basis is written down to fair value through income. For debt securities available-for-sale that do not meet the aforementioned criteria, the Company evaluates whether the decline in fair value has resulted from credit losses or other factors. In making this assessment, management considers the extent to which fair value is less than amortized cost, any changes to the rating of the security by a rating agency and adverse conditions specifically related to the security, among other factors. If this assessment indicates that a credit loss exists, the present value of cash flows expected to be collected from the security are compared to the amortized cost basis of the security.

If the present value of cash flows expected to be collected is less than the amortized cost basis, a credit loss exists and an allowance for credit losses is recorded, limited by the amount that the fair value is less than the amortized cost basis. Any impairment that has not been recorded through an allowance for credit loss is recognized in other comprehensive income. Changes in the allowance for credit losses are recorded as provision for credit loss expense. Losses are charged against the allowance when management believes the uncollectibility of an available-for-sale security is confirmed or when either of the criteria regarding intent or requirement to sell is met. Accrued interest receivable on available-for-sale debt securities, which totaled $11.7 million as of September 30, 2020, is excluded from the estimate of credit losses.

Allowance for credit losses - loans and leases. The allowance for credit losses is a valuation account that is deducted from the loans’ amortized cost basis to present the net amount expected to be collected on the loans. Management's determination of the adequacy of the ACL is based on an assessment of the expected credit losses on loan and leases over the expected life of the loan. The ACL is increased by provision expense and decreased by charge-offs, net of recoveries of amounts previously charged-off. Loans are charged off when management believes that the collection of the principal amount owed in full, either through payments from the borrower or a guarantor or from the liquidation of collateral, is unlikely. Expected recoveries do not exceed the aggregate of amounts previously charged-off and expected to be charged-off. Any interest that is accrued but not collected is reversed against interest income when a loan is placed on nonaccrual status, which typically occurs prior to charging off all, or a portion, of a loan. The Company made the policy election to exclude accrued interest receivable on loans and leases from the estimate of credit losses.

Management estimates the allowance balance using relevant available information from both internal and external sources, relating to past events, current conditions and reasonable and supportable forecasts. Historical credit loss experience paired with economic forecasts provide the basis for the quantitatively modeled estimation of expected credit losses. First Financial adjusts its quantitative model, as necessary, to reflect conditions not already considered by the quantitative model. These adjustments are commonly known as the Qualitative Framework.

First Financial quantitatively models expected credit loss using PD, LGD and EAD over the R&S forecast period, reversion and post-reversion periods.

Utilizing third-party software, the Bank forecasts PD by using a parameterized transition matrix approach. Average transition matrices are calculated over the TTC period, which was defined as the period from December 2007 to December 2016. TTC transition matrices are adjusted under forward-looking macroeconomic expectations to obtain R&S forecasts.

First Financial is not required to develop forecasts over full the contractual term of the financial asset or group of financial assets. Rather, for periods beyond which the entity is able to make or obtain R&S forecasts of expected credit losses, the Company reverts in a straight line manner over a one year period to an average TTC loss level that is reflective of the

prepayment adjusted contractual term of the financial asset or group of financial assets. The R&S period, elected by the bank to be two years, is forecasted using econometric data sourced from Moody's, an industry-leading independent third party.

FFB utilizes a non-parametric loss curve approach embedded within a third-party software for estimating LGD. The PD multiplied by LGD produces an expected loss rate that, when calculating the ACL, is applied to contractual loan cash flows, adjusted for expected future rates of principal prepayments.

The Company adjusts its quantitative model for certain qualitative factors to reflect the extent to which management expects current conditions and R&S forecasts to differ from the conditions that existed for the period over which historical information was evaluated. The Qualitative Framework reflects changes related to relevant data, such as changes in asset quality trends, portfolio growth and composition, national and local economic factors, credit policy and administration and other factors not considered in the base quantitative model.

Loans that do not share risk characteristics are evaluated on an individual basis. First Financial will typically evaluate on an individual basis any loans that are on nonaccrual, designated as a TDR, or reasonably expected to be designated as a TDR. When management determines that foreclosure is probable or when repayment is expected to be provided substantially through the operation or sale of underlying collateral, expected credit losses are based on the fair value of the collateral at the reporting date, adjusted for selling costs. For loans evaluated on an individual basis that are not determined to be collateral dependent, a discounted cash flow analysis is performed to determine expected credit losses.

Prior to the adoption of ASC 326, First Financial maintained its reserve to absorb probable losses incurred in standby letters of credit and outstanding loan commitments. First Financial determined the adequacy of this reserve based upon an evaluation of the unfunded credit facilities, which included consideration of historical commitment utilization experience, credit risk ratings and historical loss rates, consistent with the Company's ALLL methodology at the time.

Basis of Presentation Policy

Use of Estimates, Policy

Investment, Policy [Policy Text Block]

Investment securities are classified as HTM when First Financial has the positive intent and ability to hold the securities to maturity. HTM securities are recorded at amortized cost.

Credit Loss, Financial Instrument [Policy Text Block]

Loans and Leases Receivable, Allowance for Loan Losses Policy

First Financial quantitatively models expected credit loss using PD, LGD and EAD over the R&S forecast period, reversion and post-reversion periods.

Expected credit losses are estimated over the contractual term of the loans, adjusted for expected prepayments when appropriate. The contractual term excludes expected extensions, renewals and modifications unless either of the following applies: management has a reasonable expectation at the reporting date that a troubled debt restructuring will be executed with an individual borrower or the extension or renewal options are included in the original or modified contract at the reporting date and are not unconditionally cancellable by the Company. Credit card receivables do not have stated maturities. In determining the estimated life of a credit card receivable, management first estimates the future cash flows expected to be received and then applies those expected future cash flows to the credit card balance.The allowance for credit losses is a valuation account that is deducted from the loans’ amortized cost basis to present the net amount expected to be collected on the loans. The ACL is increased by provision expense and decreased by charge-offs, net of recoveries of amounts previously charged-off. First Financial's policy is to charge-off all or a portion of a loan when, in management's opinion, it is unlikely to collect the principal amount owed in full

either through payments from the borrower or a guarantor or from the liquidation of collateral. Expected recoveries do not exceed the aggregate of amounts previously charged-off and expected to be charged-off. Accrued interest receivable on loans and leases, which totaled $41.2 million as of September 30, 2020, is excluded from the estimate of credit losses.

Management estimates the allowance balance using relevant available information from both internal and external sources, relating to past events, current conditions and reasonable and supportable forecasts. Historical credit loss experience paired with economic forecasts provides the basis for the quantitatively modeled estimation of expected credit losses. First Financial adjusts its quantitative model, as necessary, to reflect conditions not already considered by the quantitative model. These adjustments are commonly known as the Qualitative Framework.

The allowance for credit losses is measured on a collective (pool) basis when similar risk characteristics exist.

Commitments and Contingencies, Policy

Allowance for credit losses - unfunded commitments. Effective January 1, 2020, First Financial adopted ASC 326, at which time First Financial estimated expected credit losses over the contractual period in which the Company is exposed to credit risk via a contractual obligation to extend credit, unless that obligation is unconditionally cancellable by the Company. The estimate includes consideration of the likelihood that funding will occur and an estimate of expected credit losses on commitments expected to be funded over its estimated life consistent with the Company's ACL methodology for loans and leases. Adjustments to the reserve for unfunded commitments are recorded in Provision for credit losses - unfunded commitments in the Consolidated Statements of Income.Prior to the adoption of ASC 326, First Financial maintained its reserve to absorb probable losses incurred in standby letters of credit and outstanding loan commitments. First Financial determined the adequacy of this reserve based upon an evaluation of the unfunded credit facilities, which included consideration of historical commitment utilization experience, credit risk ratings and historical loss rates, consistent with the Company's ALLL methodology at the time.

First Financial offers a variety of financial instruments including loan commitments and letters of credit to assist clients in meeting their requirement for liquidity and credit enhancement. GAAP does not require these financial instruments to be recorded in the Consolidated Financial Statements.

First Financial utilizes the same credit policies in issuing commitments and conditional obligations as it does for credit instruments recorded on the Consolidated Balance Sheets. First Financial’s exposure to credit loss in the event of non-performance by the counterparty was represented by the contractual amounts of those instruments. Effective January 1, 2020, First Financial adopted ASC 326, at which time First Financial estimated expected credit losses over the contractual period in which the Company is exposed to credit risk via a contractual obligation to extend credit, unless that obligation is unconditionally cancellable by the Company. The estimate includes consideration of the likelihood that funding will occur and an estimate of expected credit losses on commitments expected to be funded over its estimated life consistent with the Company's ACL methodology for loans and leases. Adjustments to the reserve for unfunded commitments are recorded in Provision for credit losses - unfunded commitments in the Consolidated Statements of Income. First Financial had $14.8 million of ACL for unfunded commitments recorded in Accrued interest and other liabilities on the Consolidated Balance Sheets as of September 30, 2020.