The allowance for loan losses is maintained at a level estimated by management to provide adequately for probable incurred losses inherent in the current loan portfolio. The appropriateness of the allowance for loan losses is continuously monitored. It is assessed for appropriateness using a methodology designed to ensure the level of the allowance reasonably reflects the loan portfolio’s risk profile and can absorb all reasonably estimable credit losses inherent in the current loan portfolio.

To develop and document a systematic methodology for determining the allowance for loan losses, the Company has divided the loan portfolio into three segments, each with different risk characteristics and methodologies for assessing risk. Those segments are further segregated between our loans accounted for under the amortized cost method (referred to as “originated” loans) and loans acquired in a business combination (referred to as “acquired” loans). Each portfolio segment is broken down into class segments where appropriate. Class segments contain unique measurement attributes, risk characteristics and methods for monitoring and assessing risk that are necessary to develop the allowance for loan losses. Unique characteristics such as borrower type, loan type, collateral type and risk characteristics define each class segment.

During the first quarter of 2018, the Company made adjustments to the class segments within the portfolios to better align risk characteristics and reflect the monitoring and assessment of risks as the portfolios continue to evolve. Agricultural and Agricultural Real Estate were consolidated with Commercial and Industrial and Commercial Real Estate, respectively. Agricultural loans are a type of Commercial loan with some specific underwriting guidelines; however, as of March 31, 2018, the portfolio had decreased to less than 3% of the Commercial portfolio and separation was no longer warranted. The Indirect class segment was further separated into Indirect Auto and Specialty Lending class segments. The growth in our Specialty Lending portfolio to 21% of Consumer Loans as of March 31, 2018 warranted evaluation of this class separately due to different risk characteristics from Indirect Auto class segments. The Direct and Home Equity class segments were consolidated into Direct to reflect common management, similar underwriting and in-market focus. The change to the class segments in the allowance methodology did not have a significant impact on the allowance for loan losses. The following table illustrates the portfolio and class segments for the Company’s loan portfolio in 2019 and 2018 compared to 2017:

Commercial and Industrial ("C&I") – The Company offers a variety of loan options to meet the specific needs of our C&I customers including term loans, time notes and lines of credit. Such loans are made available to businesses for working capital needs such as inventory and receivables, business expansion, equipment purchases, livestock purchases and seasonal crop expenses. These loans typically are usually collateralized by business assets such as equipment, accounts receivable and perishable agricultural products, which are exposed to industry price volatility. To reduce these risks, management also attempts to obtain personal guarantees of the owners or obtain government loan guarantees to provide further support. In 2018, the Commercial and Agricultural class segments were combined to create the C&I class segment.

Commercial Real Estate ("CRE") – The Company offers CRE loans to finance real estate purchases, refinancings, expansions and improvements to commercial and agricultural properties. CRE loans are loans are secured by liens on the real estate, which may include both owner occupied and non-owner-occupied properties, such as apartments, commercial structures, health care facilities and other facilities. The Company's underwriting analysis includes credit verification, independent appraisals, a review of the borrower's financial condition and a detailed analysis of the borrower's underlying cash flows. These loans are typically originated in amounts of no more than 80% of the appraised value of the property. Government loan guarantees may be obtained to provide further support for agricultural property. In 2018, the Commercial Real Estate and Agricultural Real Estate class segments were combined to create the CRE segment.

Business Banking – The Company offers a variety of loan options to meet the specific needs of our Business Banking customers including term loans, mortgages and lines of credit. Such loans are generally less than $1.0 million and are made available to businesses for working capital such as inventory and receivables, business expansion, equipment purchases and agricultural needs. Generally, a collateral lien is placed on assets owned by the borrower and can include real estate, equipment, inventory, receivables or other business assets. These loans carry a higher risk than C&I and CRE loans due to the smaller size of the borrower and lower levels of capital.

Indirect Auto – The Company maintains relationships with many dealers primarily in the communities that we serve. Through these relationships, the Company primarily finances the purchases of automobiles indirectly through dealer relationships. Approximately 95% of the Indirect Auto relationships represent automobile financing. Most of these loans carry a fixed rate of interest with principal repayment terms typically ranging from three to six years, based upon the nature of the collateral and the size of the loan. The majority of Indirect Auto Consumer loans are underwritten on a secured basis using the underlying collateral being financed. In 2018, the Indirect class segment was further separated into Indirect Auto and Specialty Lending class segments (see above and below).

Specialty Lending – The Company offers unsecured Consumer loans across a national footprint originated through our relationships with national technology-driven consumer lending companies to finance such things as dental and medical procedures, K-12 tuition, solar energy installations and other consumer purpose loans. Advances of credit through this specialty lending business line are subject to the Company's underwriting standards including criteria such as FICO score and debt to income thresholds. In 2018, the Indirect class segment has been further separated into Indirect Auto (see above) and Specialty Lending class segments.

Direct – The Company offers a variety of consumer installment loans to finance vehicle purchases, mobile home purchases and personal expenditures. In addition to installment loans, the Company also offers personal lines of credit, overdraft protection, home equity lines of credit and second mortgage loans (loans secured by a lien position on one-to-four family residential real estate) to finance home improvements, debt consolidation, education and other uses. For home equity loans, consumers are able to borrow up to 85% of the equity in their homes, and are generally tied to Prime with a ten year draw followed by a fifteen year amortization. These loans carry a higher risk than first mortgage residential loans as they are often in a second position with respect to collateral. Consumer installment loans carry a fixed rate of interest with principal repayment terms typically ranging from one to ten years, based upon the nature of the collateral and the size of the loan. Consumer installment loans are often secured with collateral consisting of a perfected lien on the asset being purchased or a perfected lien on a consumer's deposit account. Risk is reduced through underwriting criteria, which include credit verification, appraisals, a review of the borrower's financial condition and personal cash flows. A security interest, with title insurance when necessary, is taken in the underlying real estate. In 2018, the Home Equity segment was consolidated into the Direct class segment.

Residential real estate loans consist primarily of loans secured by a first or second mortgage on primary residences. We originate adjustable-rate and fixed-rate, one-to-four-family residential real estate loans for the construction, purchase or refinancing of a mortgage. These loans are collateralized by properties located in the Company’s market area. When market conditions are favorable, for longer term, fixed-rate residential real estate mortgages without escrow, the Company retains the servicing, but sells the right to receive principal and interest to Government-sponsored enterprises. This practice allows the Company to manage interest rate risk, liquidity risk and credit risk. Loans on one-to-four-family residential real estate are generally originated in amounts of no more than 85% of the purchase price or appraised value (whichever is lower) or have private mortgage insurance. Mortgage title insurance and hazard insurance are normally required. Construction loans have a unique risk, because they are secured by an incomplete dwelling. This risk is reduced through periodic site inspections, including one at each loan draw period.

For purposes of evaluating the adequacy of the allowance, the Company considers a number of significant factors that affect the collectability of the portfolio. For individually impaired loans, these include estimates of impairment, if any, which reflect the facts and circumstances that affect the likelihood of repayment of such loans as of the evaluation date. For homogeneous pools of loans, estimates of the Company’s exposure to credit loss reflect a current assessment of a number of factors, which could affect collectability. These factors include: past loss experience, size, trend, composition and nature of loans; changes in lending policies and procedures, including underwriting standards and collection, charge-offs and recoveries; trends experienced in nonperforming and delinquent loans; current economic conditions in the Company’s market; portfolio concentrations that may affect loss experienced across one or more components of the portfolio; the effect of external factors such as competition, legal and regulatory requirements; and the experience, ability and depth of lending management and staff. In addition, various regulatory agencies, as an integral component of their examination process, periodically review the Company’s allowance for loan losses. Such agencies may require the Company to make loan grade changes as well as recognize additions to the allowance based on their examinations.

After a thorough consideration of the factors discussed above, any required additions or reductions to the allowance for loan losses are made periodically by charges or credits to the provision for loan losses. These charges are necessary to maintain the allowance at a level that management believes is reflective of overall level of incurred loss in the portfolio. While management uses available information to recognize losses on loans, additions and reductions of the allowance may fluctuate from one reporting period to another. These fluctuations are reflective of changes in risk associated with portfolio content or changes in management’s assessment of any or all of the determining factors discussed above.

For acquired loans, to the extent that we experience deterioration in borrower credit quality resulting in a decrease in our expected cash flows subsequent to the acquisition of the loans, an allowance for loan losses is established based on our estimate of incurred losses at the balance sheet date. There was no allowance for loan losses for the acquired loan portfolio as of December 31, 2019 and 2018. Net charge-offs related to acquired loans totaled approximately $0.1 million, $0.1 million and $0.7 million during the years ended December 31, 2019, 2018 and 2017, respectively, and are included in the table above.

The methodology used to establish the allowance for loan losses on impaired loans incorporates specific allocations on loans analyzed individually. Classified loans, including all TDRs and nonaccrual Commercial loans that are graded Substandard, Doubtful or Loss, with outstanding balances of $1.0 million or more are evaluated for impairment through the Company’s quarterly status review process. The Company considers Commercial loans less than $1.0 million to be homogeneous loans. In the third quarter of 2019 the threshold for evaluating loans for impairment was increased from $750 thousand. In determining that we will be unable to collect all principal and/or interest payments due in accordance with the contractual terms of the loan agreements, we consider factors such as payment history and changes in the financial condition of individual borrowers, local economic conditions, historical loss experience and the conditions of the various markets in which the collateral may be liquidated. For loans that are identified as impaired, impairment is measured by one of three methods: 1) the fair value of collateral less cost to sell, 2) present value of expected future cash flows or 3) the loan’s observable market price. These impaired loans are reviewed on a quarterly basis for changes in the level of impairment. Impaired amounts are charged off immediately if such amounts are determined by management to be uncollectable. Any change to the previously recognized impairment loss is recognized as a component of the provision for loan losses.

The Company has developed an internal loan grading system to evaluate and quantify the Company’s loan portfolio with respect to quality and risk. The system focuses on, among other things, financial strength of borrowers, experience and depth of borrower’s management, primary and secondary sources of repayment, payment history, nature of the business and outlook on particular industries. The internal grading system enables the Company to monitor the quality of the entire loan portfolio on a consistent basis and provide management with an early warning system, enabling recognition and response to problem loans and potential problem loans.

For C&I and CRE loans, the Company uses a grading system that relies on quantifiable and measurable characteristics when available. This includes comparison of financial strength to available industry averages, comparison of transaction factors (loan terms and conditions) to loan policy and comparison of credit history to stated repayment terms and industry averages. Some grading factors are necessarily more subjective such as economic and industry factors, regulatory environment and management. C&I and CRE loans are graded Doubtful, Substandard, Special Mention and Pass.

A Doubtful loan has a high probability of total or substantial loss, but because of specific pending events that may strengthen the asset, its classification as a loss is deferred. Doubtful borrowers are usually in default, lack adequate liquidity or capital and lack the resources necessary to remain an operating entity. Pending events can include mergers, acquisitions, liquidations, capital injections, the perfection of liens on additional collateral, the valuation of collateral and refinancing. Generally, pending events should be resolved within a relatively short period and the ratings will be adjusted based on the new information. Nonaccrual treatment is required for Doubtful assets because of the high probability of loss.

Substandard loans have a high probability of payment default or they have other well-defined weaknesses. They require more intensive supervision by bank management. Substandard loans are generally characterized by current or expected unprofitable operations, inadequate debt service coverage, inadequate liquidity or marginal capitalization. Repayment may depend on collateral or other credit risk mitigants. For some Substandard loans, the likelihood of full collection of interest and principal may be in doubt and those loans should be placed on nonaccrual. Although Substandard assets in the aggregate will have a distinct potential for loss, an individual asset’s loss potential does not have to be distinct for the asset to be rated Substandard.

Special Mention loans have potential weaknesses that may, if not checked or corrected, weaken the asset or inadequately protect the Company’s position at some future date. These loans pose elevated risk, but their weakness does not yet justify a Substandard classification. Borrowers may be experiencing adverse operating trends (i.e., declining revenues or margins) or may be struggling with an ill-proportioned balance sheet (i.e., increasing inventory without an increase in sales, high leverage, tight liquidity). Adverse economic or market conditions, such as interest rate increases or the entry of a new competitor, may also support a Special Mention rating. Although a Special Mention loan has a higher probability of default than a Pass asset, its default is not imminent.

Classified loans are inadequately protected by the current worth and paying capacity of the obligor or, if applicable, the collateral pledged. These loans have a well-defined weakness or weaknesses, that jeopardize the liquidation of the debt or in some cases make collection or liquidation in full, on the basis of currently existing facts, conditions and values, highly questionable and improbable. They are characterized by the distinct possibility that the Company will sustain some loss if the deficiencies are not corrected. Classified loans have a high probability of payment default or a substantial loss. These loans require more intensive supervision by management and are generally characterized by current or expected unprofitable operations, inadequate debt service coverage, inadequate liquidity or marginal capitalization. Repayment may depend on collateral or other credit risk mitigants. Classified loans where the full collection of interest and principal is in doubt are considered to have a nonaccrual status. In some cases, Classified loans are considered uncollectable and of such little value that their continuance as assets is not warranted.