Recent Accounting Pronouncements	9 Months Ended
Sep. 30, 2018
New Accounting Pronouncements and Changes in Accounting Principles [Abstract]
Recent Accounting Pronouncements	RECENT ACCOUNTING PRONOUNCEMENTS Adopted Accounting Pronouncements Revenue from Contracts with Customers: In May of 2014, the Financial Accounting Standards Board ("FASB") issued guidance that requires an entity to recognize revenue to depict the transfer of promised goods or services to customers in an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods or services. In March of 2016, the FASB issued an amendment to this guidance to clarify the implementation of guidance on principal versus agent consideration. Additional amendments to clarify the implementation guidance on the identification of performance obligations and licensing were issued in April of 2016 and narrow-scope improvements and practical expedients were issued in May of 2016. The guidance is effective for annual and interim reporting periods beginning on or after December 15, 2017, and must be applied either retrospectively or using the modified retrospective approach. The Company's revenue is comprised of net interest income on financial assets and liabilities, which is excluded from the scope of this guidance, and noninterest income. The primary sources of revenue within noninterest income are service charges on deposit accounts, wealth management fees, card-based fees, and merchant servicing fees. The adoption of this guidance on January 1, 2018, using the modified retrospective approach, affected how the Company presents merchant servicing fees, merchant card expenses, card-based fees, and cardholder expenses, which are presented on a gross basis within noninterest income and noninterest expense for the prior period and are presented on a net basis within noninterest income for the current period. Total expenses of $4.2 million and $11.9 million for the quarter and nine months ended September 30, 2018 were netted in noninterest income. The adoption of this guidance did not impact net income; therefore, a cumulative effect adjustment to opening retained earnings was not deemed necessary. Consistent with the modified retrospective approach, the Company did not adjust prior period amounts for the reclassification of merchant card expenses and cardholder expenses. A description of the Company's revenue streams accounted for under the scope of this guidance follows: Service charges on deposit accounts – Service charges on deposit accounts consist of account analysis fees (net fees earned on analyzed business and public checking accounts), monthly service fees, and other deposit account related fees. The Company's performance obligation for account analysis fees and monthly service fees is generally satisfied, and the related revenue recognized, over the period in which the service is provided. Other deposit account related fees are largely transactional based and, therefore, the Company's performance obligation is satisfied, and related revenue recognized, at a point in time. Payment for service charges on deposit accounts is primarily received as a direct charge to customers' accounts. As a result of the adoption of this guidance, there was no impact to the method of recognizing revenue related to service charges on deposit accounts for the quarter and nine months ended September 30, 2018. Wealth management fees – Wealth management fees represents quarterly fees due from wealth management customers as consideration for managing the customers' assets. Wealth management services include custody of assets, investment management, escrow services, fees for trust services and similar fiduciary activities. Revenue is recognized when our performance obligation is completed each quarter, which is generally the time that payment is received. Also included are fees received from a third-party broker-dealer as part of a revenue-sharing agreement. These fees are paid to us by the third-party on a quarterly basis and recognized ratably throughout the quarter as our performance obligation is satisfied. As a result of the adoption of this guidance, there was no impact to the method of recognizing revenue related to wealth management fees for the quarter and nine months ended September 30, 2018. Card-based fees, net – Card-based fees, net consists of debit and credit card interchange fees for processing transactions, as well as various fees for automated teller machine ("ATM") and point-of-sale transactions processed through the related networks. Interchange, ATM, and point-of-sale fees from cardholder transactions represent a percentage of the underlying transaction value or a flat fee and are recognized daily in connection with the transaction processing services provided to the cardholder. Card-based fees are presented net of certain contract costs associated with the debit, credit and ATM card interchange networks. As a result of the adoption of this guidance, $1.9 million and $5.5 million of cardholder expenses are netted against card-based fees for the quarter and nine months ended September 30, 2018, respectively. Merchant servicing fees, net – Merchant servicing fees, net is included in other service charges, commissions, and fees in the Consolidated Statements of Income. The Company acts in an agency capacity with respect to its merchants to process their debit and credit card transactions, deriving revenue from assisting another entity in transactions with the Company's customers. Merchant servicing fees represent a percentage of the underlying net transaction volume or a flat fee and are recognized monthly. Merchant servicing fees are presented net of certain contract costs associated with the third-party merchant processing. As a result of the adoption of this guidance, $2.3 million and $6.4 million of merchant card expenses are netted against merchant servicing fees for the quarter and nine months ended September 30, 2018, respectively. Amendments to Guidance on Classifying and Measuring Financial Instruments: In January of 2016, the FASB issued guidance that will require entities to measure equity investments that do not result in consolidation and are not accounted for under the equity method at fair value. Any subsequent changes in fair value will be recognized in net income unless the investments qualify for a new practicability exception. Equity securities totaling $29.0 million are no longer classified as trading securities or securities available-for-sale. This guidance also requires entities to adjust the fair value disclosures for financial instruments carried at amortized cost from an entry price to an exit price. No changes were made to the guidance for classifying and measuring investments in debt securities and loans. Except as discussed above, the adoption of this guidance on January 1, 2018 did not materially impact the Company's financial condition, results of operations, or liquidity. Classification of Certain Cash Receipts and Cash Payments: In August of 2016, the FASB issued guidance clarifying certain cash flow presentation and classification issues to reduce diversity in practice. The adoption of this guidance on January 1, 2018 did not materially impact the Company's financial condition, results of operations, or liquidity. Income Taxes: In October of 2016, the FASB issued guidance that requires an entity to recognize the income tax consequences of an intra-entity transfer of an asset other than inventory when the transfer occurs. The adoption of this guidance on January 1, 2018 did not materially impact the Company's financial condition, results of operations, or liquidity. Clarifying the Definition of a Business: In January of 2017, the FASB issued guidance that clarifies the definition of a business to assist entities with evaluating whether transactions should be accounted for as acquisitions or disposals of assets or businesses. The adoption of this guidance on January 1, 2018 did not impact the Company's financial condition, results of operations, or liquidity. Presentation of Defined Benefit Retirement Plan Costs: In March of 2017, the FASB issued guidance that changes how employers that sponsor defined pension and or other postretirement benefit plans present the net periodic benefit cost in the income statement. Employers are required to present the service cost component of the net periodic benefit cost in the same income statement line item as other employee compensation costs arising from services rendered during the period. Other components of net periodic benefit cost are required to be presented separately from the line item(s) that includes the service cost. The adoption of this guidance on January 1, 2018 did not materially impact the Company's financial condition, results of operations, or liquidity. Share-based Payment Award Modifications: In May of 2017, the FASB issued guidance to reduce diversity in practice by clarifying when changes to the terms or conditions of a share-based payment award must be accounted for as a modification. The adoption of this guidance on January 1, 2018 did not materially impact the Company's financial condition, results of operations, or liquidity. Derivatives and Hedging: In August of 2017, the FASB issued guidance to better align the financial reporting related to hedging activities with the economic objectives of those activities and to simplify the application of current hedge accounting guidance. Entities are required to apply the guidance using a modified retrospective method as of the period of adoption. This guidance is effective for annual and interim periods beginning after December 31, 2018. Early adoption is permitted, and the Company elected to do so on January 1, 2018, which did not materially impact the Company's financial condition, results of operations, or liquidity. Reclassification of Certain Tax Effects from Accumulated Other Comprehensive Income: In February of 2018, the FASB issued guidance that requires a reclassification from accumulated other comprehensive income to retained earnings for stranded tax effects resulting from the Tax Cuts and Jobs Act of 2017. Entities electing the reclassification are required to apply the guidance either at the beginning of the period of adoption or retrospectively for all periods impacted. This guidance is effective for annual and interim periods beginning after December 15, 2018. Early adoption is permitted and the Company elected to do so on January 1, 2018, which resulted in the reclassification of $6.8 million of stranded tax effects from accumulated other comprehensive loss to retained earnings as of the beginning of the period of adoption. Accounting Pronouncements Pending Adoption Leases: In February of 2016, the FASB issued guidance to increase transparency and comparability across entities for leasing arrangements. This guidance requires lessees to recognize assets and liabilities for most leases. For lessors, this guidance modifies the lease classification criteria and the accounting for sales-type and direct financing leases. In addition, this guidance clarifies criteria for the determination of whether a contract is or contains a lease. This guidance is effective for annual and interim periods beginning after December 15, 2018. Early adoption is permitted. The Company will adopt this guidance on January 1, 2019, which will result in the recognition of right-of-use assets and associated lease liabilities for its operating leases. The amount of right-of-use assets and associated lease liabilities recorded upon adoption will be based on the present value of future minimum lease payments, the amount of which will depend on the population of leases in effect at the date of adoption. In addition, First Midwest Bank (the "Bank") entered into a sale-leaseback transaction in 2016 that resulted in a deferred gain. Upon adoption of this guidance, the remaining deferred gain, which is estimated to be approximately $50 million after tax, will be recognized immediately as a cumulative-effect adjustment to equity. For additional discussion of the sale-leaseback transaction, see Note 8 "Premises, Furniture, and Equipment" to the Consolidated Financial Statements in the Company's 2017 10-K. Management is completing its evaluation of the guidance and does not expect the adoption of the guidance will materially impact the Company's results of operations or liquidity, but anticipates a material increase in assets, liabilities, and equity. Measurement of Credit Losses on Financial Instruments: In June of 2016, the FASB issued guidance that will require entities to present financial assets measured at amortized cost at the net amount expected to be collected, considering an entity's current estimate of all expected credit losses. In addition, credit losses relating to available-for-sale debt securities will be required to be recorded through an allowance for credit losses, with changes in credit loss estimates recognized through current earnings. This guidance is effective for annual and interim periods beginning after December 15, 2019. Early adoption is permitted, but not for periods beginning before December 15, 2018. Management is evaluating the guidance and the impact to the Company's financial condition, results of operations, or liquidity. Accounting for Goodwill Impairment: In January of 2017, the FASB issued guidance that simplifies the accounting for goodwill impairment for all entities. The new guidance eliminates the requirement to calculate the implied fair value of goodwill using the second step of the quantitative two-step goodwill impairment model prescribed under current accounting guidance. Under the new guidance, if a reporting unit's carrying amount exceeds its fair value, an entity will record an impairment charge based on that difference. This guidance is effective for annual and interim goodwill impairment testing dates beginning after December 15, 2019. Early adoption is permitted for annual and interim goodwill impairment testing dates after January 1, 2017. Management does not expect the adoption of this guidance will materially impact the Company's financial condition, results of operations, or liquidity. Premium Amortization on Purchased Callable Debt Securities: In March of 2017, the FASB issued guidance that shortens the amortization period for the premium on certain purchased callable debt securities to the earliest call date. This guidance is effective for annual and interim periods beginning after December 15, 2018. Early adoption is permitted. Management does not expect the adoption of this guidance will materially impact the Company's financial condition, results of operations, or liquidity. Improvements to Nonemployee Share-based Payment Accounting: In June of 2018, the FASB issued guidance that aligns the measurement and classification guidance for share-based payments to nonemployees with the guidance for share-based payments to employees. This guidance is effective for annual and interim periods beginning after December 15, 2018. Early adoption is permitted. Management does not expect the adoption of this guidance will materially impact the Company's financial condition, results of operations, or liquidity. Changes to the Disclosure Requirements for Fair Value Measurement: In August of 2018, the FASB issued guidance that eliminates, modifies, and adds to certain fair value measurement disclosure requirements associated with the three-tiered fair value hierarchy. This guidance is effective for annual and interim periods beginning after December 15, 2019. Early adoption is permitted. Management does not expect the adoption of this guidance will materially impact the Company's financial condition, results of operations, or liquidity. Changes to the Disclosure Requirements for Defined Benefit Plans: In August of 2018, the FASB issued guidance that makes minor changes and clarifications to the disclosure requirements for entities that sponsor defined benefit plans. This guidance is effective for annual and interim periods beginning after December 15, 2020. Early adoption is permitted. Management does not expect the adoption of this guidance will materially impact the Company's financial condition, results of operations, or liquidity. Customer's Accounting for Implementation Costs Incurred in a Cloud Computing Arrangement That Is a Service Contract: In August of 2018, the FASB issued guidance to reduce diversity in practice by clarifying when implementation costs are required to be capitalized in a cloud computing arrangement that is a service contract. This guidance is effective for annual and interim periods beginning after December 15, 2019. Early adoption is permitted. Management does not expect the adoption of this guidance will materially impact the Company's financial condition, results of operations, or liquidity.

RECENT ACCOUNTING PRONOUNCEMENTS

Adopted Accounting Pronouncements

Revenue from Contracts with Customers: In May of 2014, the Financial Accounting Standards Board ("FASB") issued guidance that requires an entity to recognize revenue to depict the transfer of promised goods or services to customers in an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods or services. In March of 2016, the FASB issued an amendment to this guidance to clarify the implementation of guidance on principal versus agent consideration. Additional amendments to clarify the implementation guidance on the identification of performance obligations and licensing were issued in April of 2016 and narrow-scope improvements and practical expedients were issued in May of 2016. The guidance is effective for annual and interim reporting periods beginning on or after December 15, 2017, and must be applied either retrospectively or using the modified retrospective approach.

The Company's revenue is comprised of net interest income on financial assets and liabilities, which is excluded from the scope of this guidance, and noninterest income. The primary sources of revenue within noninterest income are service charges on deposit accounts, wealth management fees, card-based fees, and merchant servicing fees. The adoption of this guidance on January 1, 2018, using the modified retrospective approach, affected how the Company presents merchant servicing fees, merchant card expenses, card-based fees, and cardholder expenses, which are presented on a gross basis within noninterest income and noninterest expense for the prior period and are presented on a net basis within noninterest income for the current period. Total expenses of $4.2 million and $11.9 million for the quarter and nine months ended September 30, 2018 were netted in noninterest income. The adoption of this guidance did not impact net income; therefore, a cumulative effect adjustment to opening retained earnings was not deemed necessary. Consistent with the modified retrospective approach, the Company did not adjust prior period amounts for the reclassification of merchant card expenses and cardholder expenses.

A description of the Company's revenue streams accounted for under the scope of this guidance follows:

Service charges on deposit accounts – Service charges on deposit accounts consist of account analysis fees (net fees earned on analyzed business and public checking accounts), monthly service fees, and other deposit account related fees. The Company's performance obligation for account analysis fees and monthly service fees is generally satisfied, and the related revenue recognized, over the period in which the service is provided. Other deposit account related fees are largely transactional based and, therefore, the Company's performance obligation is satisfied, and related revenue recognized, at a point in time. Payment for service charges on deposit accounts is primarily received as a direct charge to customers' accounts. As a result of the adoption of this guidance, there was no impact to the method of recognizing revenue related to service charges on deposit accounts for the quarter and nine months ended September 30, 2018.

Wealth management fees – Wealth management fees represents quarterly fees due from wealth management customers as consideration for managing the customers' assets. Wealth management services include custody of assets, investment management, escrow services, fees for trust services and similar fiduciary activities. Revenue is recognized when our performance obligation is completed each quarter, which is generally the time that payment is received. Also included are fees received from a third-party broker-dealer as part of a revenue-sharing agreement. These fees are paid to us by the third-party on a quarterly basis and recognized ratably throughout the quarter as our performance obligation is satisfied. As a result of the adoption of this guidance, there was no impact to the method of recognizing revenue related to wealth management fees for the quarter and nine months ended September 30, 2018.

Card-based fees, net – Card-based fees, net consists of debit and credit card interchange fees for processing transactions, as well as various fees for automated teller machine ("ATM") and point-of-sale transactions processed through the related networks. Interchange, ATM, and point-of-sale fees from cardholder transactions represent a percentage of the underlying transaction value or a flat fee and are recognized daily in connection with the transaction processing services provided to the cardholder. Card-based fees are presented net of certain contract costs associated with the debit, credit and ATM card interchange networks. As a result of the adoption of this guidance, $1.9 million and $5.5 million of cardholder expenses are netted against card-based fees for the quarter and nine months ended September 30, 2018, respectively.

Merchant servicing fees, net – Merchant servicing fees, net is included in other service charges, commissions, and fees in the Consolidated Statements of Income. The Company acts in an agency capacity with respect to its merchants to process their debit and credit card transactions, deriving revenue from assisting another entity in transactions with the Company's customers. Merchant servicing fees represent a percentage of the underlying net transaction volume or a flat fee and are recognized monthly. Merchant servicing fees are presented net of certain contract costs associated with the third-party merchant processing. As a result of the adoption of this guidance, $2.3 million and $6.4 million of merchant card expenses are netted against merchant servicing fees for the quarter and nine months ended September 30, 2018, respectively.

Amendments to Guidance on Classifying and Measuring Financial Instruments: In January of 2016, the FASB issued guidance that will require entities to measure equity investments that do not result in consolidation and are not accounted for under the equity method at fair value. Any subsequent changes in fair value will be recognized in net income unless the investments qualify for a new practicability exception. Equity securities totaling $29.0 million are no longer classified as trading securities or securities available-for-sale. This guidance also requires entities to adjust the fair value disclosures for financial instruments carried at amortized cost from an entry price to an exit price. No changes were made to the guidance for classifying and measuring investments in debt securities and loans. Except as discussed above, the adoption of this guidance on January 1, 2018 did not materially impact the Company's financial condition, results of operations, or liquidity.

Classification of Certain Cash Receipts and Cash Payments: In August of 2016, the FASB issued guidance clarifying certain cash flow presentation and classification issues to reduce diversity in practice. The adoption of this guidance on January 1, 2018 did not materially impact the Company's financial condition, results of operations, or liquidity.

Income Taxes: In October of 2016, the FASB issued guidance that requires an entity to recognize the income tax consequences of an intra-entity transfer of an asset other than inventory when the transfer occurs. The adoption of this guidance on January 1, 2018 did not materially impact the Company's financial condition, results of operations, or liquidity.

Clarifying the Definition of a Business: In January of 2017, the FASB issued guidance that clarifies the definition of a business to assist entities with evaluating whether transactions should be accounted for as acquisitions or disposals of assets or businesses. The adoption of this guidance on January 1, 2018 did not impact the Company's financial condition, results of operations, or liquidity.

Presentation of Defined Benefit Retirement Plan Costs: In March of 2017, the FASB issued guidance that changes how employers that sponsor defined pension and or other postretirement benefit plans present the net periodic benefit cost in the income statement. Employers are required to present the service cost component of the net periodic benefit cost in the same income statement line item as other employee compensation costs arising from services rendered during the period. Other components of net periodic benefit cost are required to be presented separately from the line item(s) that includes the service cost. The adoption of this guidance on January 1, 2018 did not materially impact the Company's financial condition, results of operations, or liquidity.

Share-based Payment Award Modifications: In May of 2017, the FASB issued guidance to reduce diversity in practice by clarifying when changes to the terms or conditions of a share-based payment award must be accounted for as a modification. The adoption of this guidance on January 1, 2018 did not materially impact the Company's financial condition, results of operations, or liquidity.

Derivatives and Hedging: In August of 2017, the FASB issued guidance to better align the financial reporting related to hedging activities with the economic objectives of those activities and to simplify the application of current hedge accounting guidance. Entities are required to apply the guidance using a modified retrospective method as of the period of adoption. This guidance is effective for annual and interim periods beginning after December 31, 2018. Early adoption is permitted, and the Company elected to do so on January 1, 2018, which did not materially impact the Company's financial condition, results of operations, or liquidity.

Reclassification of Certain Tax Effects from Accumulated Other Comprehensive Income: In February of 2018, the FASB issued guidance that requires a reclassification from accumulated other comprehensive income to retained earnings for stranded tax effects resulting from the Tax Cuts and Jobs Act of 2017. Entities electing the reclassification are required to apply the guidance either at the beginning of the period of adoption or retrospectively for all periods impacted. This guidance is effective for annual and interim periods beginning after December 15, 2018. Early adoption is permitted and the Company elected to do so on January 1, 2018, which resulted in the reclassification of $6.8 million of stranded tax effects from accumulated other comprehensive loss to retained earnings as of the beginning of the period of adoption.

Accounting Pronouncements Pending Adoption

Leases: In February of 2016, the FASB issued guidance to increase transparency and comparability across entities for leasing arrangements. This guidance requires lessees to recognize assets and liabilities for most leases. For lessors, this guidance modifies the lease classification criteria and the accounting for sales-type and direct financing leases. In addition, this guidance clarifies criteria for the determination of whether a contract is or contains a lease. This guidance is effective for annual and interim periods beginning after December 15, 2018. Early adoption is permitted.

The Company will adopt this guidance on January 1, 2019, which will result in the recognition of right-of-use assets and associated lease liabilities for its operating leases. The amount of right-of-use assets and associated lease liabilities recorded upon adoption will be based on the present value of future minimum lease payments, the amount of which will depend on the population of leases in effect at the date of adoption. In addition, First Midwest Bank (the "Bank") entered into a sale-leaseback transaction in 2016 that resulted in a deferred gain. Upon adoption of this guidance, the remaining deferred gain, which is estimated to be approximately $50 million after tax, will be recognized immediately as a cumulative-effect adjustment to equity. For additional discussion of the sale-leaseback transaction, see Note 8 "Premises, Furniture, and Equipment" to the Consolidated Financial Statements in the Company's 2017 10-K. Management is completing its evaluation of the guidance and does not expect the adoption of the guidance will materially impact the Company's results of operations or liquidity, but anticipates a material increase in assets, liabilities, and equity.

Measurement of Credit Losses on Financial Instruments: In June of 2016, the FASB issued guidance that will require entities to present financial assets measured at amortized cost at the net amount expected to be collected, considering an entity's current estimate of all expected credit losses. In addition, credit losses relating to available-for-sale debt securities will be required to be recorded through an allowance for credit losses, with changes in credit loss estimates recognized through current earnings. This guidance is effective for annual and interim periods beginning after December 15, 2019. Early adoption is permitted, but not for periods beginning before December 15, 2018. Management is evaluating the guidance and the impact to the Company's financial condition, results of operations, or liquidity.

Accounting for Goodwill Impairment: In January of 2017, the FASB issued guidance that simplifies the accounting for goodwill impairment for all entities. The new guidance eliminates the requirement to calculate the implied fair value of goodwill using the second step of the quantitative two-step goodwill impairment model prescribed under current accounting guidance. Under the new guidance, if a reporting unit's carrying amount exceeds its fair value, an entity will record an impairment charge based on that difference. This guidance is effective for annual and interim goodwill impairment testing dates beginning after December 15, 2019. Early adoption is permitted for annual and interim goodwill impairment testing dates after January 1, 2017. Management does not expect the adoption of this guidance will materially impact the Company's financial condition, results of operations, or liquidity.

Premium Amortization on Purchased Callable Debt Securities: In March of 2017, the FASB issued guidance that shortens the amortization period for the premium on certain purchased callable debt securities to the earliest call date. This guidance is effective for annual and interim periods beginning after December 15, 2018. Early adoption is permitted. Management does not expect the adoption of this guidance will materially impact the Company's financial condition, results of operations, or liquidity.

Improvements to Nonemployee Share-based Payment Accounting: In June of 2018, the FASB issued guidance that aligns the measurement and classification guidance for share-based payments to nonemployees with the guidance for share-based payments to employees. This guidance is effective for annual and interim periods beginning after December 15, 2018. Early adoption is permitted. Management does not expect the adoption of this guidance will materially impact the Company's financial condition, results of operations, or liquidity.

Changes to the Disclosure Requirements for Fair Value Measurement: In August of 2018, the FASB issued guidance that eliminates, modifies, and adds to certain fair value measurement disclosure requirements associated with the three-tiered fair value hierarchy. This guidance is effective for annual and interim periods beginning after December 15, 2019. Early adoption is permitted. Management does not expect the adoption of this guidance will materially impact the Company's financial condition, results of operations, or liquidity.

Changes to the Disclosure Requirements for Defined Benefit Plans: In August of 2018, the FASB issued guidance that makes minor changes and clarifications to the disclosure requirements for entities that sponsor defined benefit plans. This guidance is effective for annual and interim periods beginning after December 15, 2020. Early adoption is permitted. Management does not expect the adoption of this guidance will materially impact the Company's financial condition, results of operations, or liquidity.

Customer's Accounting for Implementation Costs Incurred in a Cloud Computing Arrangement That Is a Service Contract: In August of 2018, the FASB issued guidance to reduce diversity in practice by clarifying when implementation costs are required to be capitalized in a cloud computing arrangement that is a service contract. This guidance is effective for annual and interim periods beginning after December 15, 2019. Early adoption is permitted. Management does not expect the adoption of this guidance will materially impact the Company's financial condition, results of operations, or liquidity.