Recent Accounting Pronouncements	9 Months Ended
Sep. 30, 2017
New Accounting Pronouncements and Changes in Accounting Principles [Abstract]
Recent Accounting Pronouncements	RECENT ACCOUNTING PRONOUNCEMENTS Adopted Accounting Pronouncements Contingent Put and Call Options in Debt Instruments: In March of 2016, the Financial Accounting Standards Board ("FASB") issued final guidance clarifying the requirements for assessing whether contingent call (put) options that can accelerate the payment of principal on debt instruments are clearly and closely related to their debt hosts. Entities are required to apply the guidance to existing debt instruments (or hybrid financial instruments that are determined to have a debt host) using a modified retrospective transition method as of the period of adoption. The adoption of this guidance on January 1, 2017 did not impact the Company's financial condition, results of operations, or liquidity. Equity Method Accounting: In March of 2016, the FASB issued final guidance to simplify the equity method of accounting. The guidance eliminates the requirement to retrospectively apply equity method accounting in previous periods when an investor initially obtains significant influence over an investee. This guidance is effective for annual and interim periods beginning after December 15, 2016. The adoption of this guidance on January 1, 2017 did not impact the Company's financial condition, results of operations, or liquidity. Accounting for Employee Share-based Payments: In March of 2016, the FASB issued guidance to simplify the accounting for employee share-based payment transactions. The guidance requires entities to recognize the income tax effects of awards in the income statement when the awards vest or are settled. In addition, the guidance allows entities to repurchase more of an employee's shares than it can under current guidance for tax withholding purposes without triggering liability accounting and to make a policy election to account for forfeitures as they occur. The adoption of this guidance on January 1, 2017 resulted in a $638,000 tax benefit to the provision for income tax expense for the nine months ended September 30, 2017, recorded in the Company's results of operations. The Company elected to estimate forfeitures, which is consistent with the Company's practice before the adoption of this guidance. Accounting Pronouncements Pending Adoption Revenue from Contracts with Customers: In May of 2014, the 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 was initially effective for annual and interim reporting periods beginning on or after December 15, 2016 but was deferred to December 15, 2017, and must be applied either retrospectively or using the modified retrospective approach. Early adoption is permitted, but not before the original effective date. 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. Based upon the Company's initial assessment, this guidance is expected to affect how the Company currently presents certain contract costs on a gross basis versus a net basis against the related noninterest income and will result in the expansion of the qualitative disclosures regarding noninterest income. The Company will adopt this guidance on January 1, 2018 using the modified retrospective approach and does not expect the changes in presentation of certain contract costs or the expanded disclosures to have a significant impact on the Company's financial condition, results of operations, or liquidity. The Company is in the process of completing its review of contracts to validate this initial assessment. 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 changes in fair value will be recognized in net income unless the investments qualify for a new practicability exception. 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. This guidance is effective for annual and interim periods beginning after December 15, 2017. 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. 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. During 2016, First Midwest Bank (the "Bank") entered into a sale-leaseback transaction that resulted in a deferred gain of $82.5 million, with $76.1 million remaining as of September 30, 2017. Upon adoption of this guidance, the remaining deferred gain 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." Management is evaluating the new guidance and the additional impact to the Company's financial condition, results of operations, or liquidity. 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 new guidance and the impact to the Company's financial condition, results of operations, and 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. This guidance is effective for annual and interim reporting periods beginning on or after December 15, 2017. Early adoption is permitted. Management does not expect the adoption of this guidance will materially impact the Company's Consolidated Statement of Cash Flows. 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. This guidance is effective for annual and interim periods beginning after December 15, 2017. 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. 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. This guidance is effective for annual and interim periods beginning after December 15, 2017. 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. 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. 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 will present the service cost component of 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 will be presented separately from the line item(s) that includes the service cost. This guidance is effective for annual and interim periods beginning after December 15, 2017. 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. 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. 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. This guidance is effective for annual and interim periods beginning after December 15, 2017. 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. 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. Management is evaluating the new guidance, but 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

Contingent Put and Call Options in Debt Instruments: In March of 2016, the Financial Accounting Standards Board ("FASB") issued final guidance clarifying the requirements for assessing whether contingent call (put) options that can accelerate the payment of principal on debt instruments are clearly and closely related to their debt hosts. Entities are required to apply the guidance to existing debt instruments (or hybrid financial instruments that are determined to have a debt host) using a modified retrospective transition method as of the period of adoption. The adoption of this guidance on January 1, 2017 did not impact the Company's financial condition, results of operations, or liquidity.

Equity Method Accounting: In March of 2016, the FASB issued final guidance to simplify the equity method of accounting. The guidance eliminates the requirement to retrospectively apply equity method accounting in previous periods when an investor initially obtains significant influence over an investee. This guidance is effective for annual and interim periods beginning after December 15, 2016. The adoption of this guidance on January 1, 2017 did not impact the Company's financial condition, results of operations, or liquidity.

Accounting for Employee Share-based Payments: In March of 2016, the FASB issued guidance to simplify the accounting for employee share-based payment transactions. The guidance requires entities to recognize the income tax effects of awards in the income statement when the awards vest or are settled. In addition, the guidance allows entities to repurchase more of an employee's shares than it can under current guidance for tax withholding purposes without triggering liability accounting and to make a policy election to account for forfeitures as they occur. The adoption of this guidance on January 1, 2017 resulted in a $638,000 tax benefit to the provision for income tax expense for the nine months ended September 30, 2017, recorded in the Company's results of operations. The Company elected to estimate forfeitures, which is consistent with the Company's practice before the adoption of this guidance.

Accounting Pronouncements Pending Adoption

Revenue from Contracts with Customers: In May of 2014, the 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 was initially effective for annual and interim reporting periods beginning on or after December 15, 2016 but was deferred to December 15, 2017, and must be applied either retrospectively or using the modified retrospective approach. Early adoption is permitted, but not before the original effective date.

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. Based upon the Company's initial assessment, this guidance is expected to affect how the Company currently presents certain contract costs on a gross basis versus a net basis against the related noninterest income and will result in the expansion of the qualitative disclosures regarding noninterest income. The Company will adopt this guidance on January 1, 2018 using the modified retrospective approach and does not expect the changes in presentation of certain contract costs or the expanded disclosures to have a significant impact on the Company's financial condition, results of operations, or liquidity. The Company is in the process of completing its review of contracts to validate this initial assessment.

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 changes in fair value will be recognized in net income unless the investments qualify for a new practicability exception. 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. This guidance is effective for annual and interim periods beginning after December 15, 2017. 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.

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.

During 2016, First Midwest Bank (the "Bank") entered into a sale-leaseback transaction that resulted in a deferred gain of $82.5 million, with $76.1 million remaining as of September 30, 2017. Upon adoption of this guidance, the remaining deferred gain 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." Management is evaluating the new guidance and the additional impact to the Company's financial condition, results of operations, or liquidity.

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 new guidance and the impact to the Company's financial condition, results of operations, and 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. This guidance is effective for annual and interim reporting periods beginning on or after December 15, 2017. Early adoption is permitted. Management does not expect the adoption of this guidance will materially impact the Company's Consolidated Statement of Cash Flows.

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. This guidance is effective for annual and interim periods beginning after December 15, 2017. 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.

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. This guidance is effective for annual and interim periods beginning after December 15, 2017. 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.

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.

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 will present the service cost component of 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 will be presented separately from the line item(s) that includes the service cost. This guidance is effective for annual and interim periods beginning after December 15, 2017. 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.

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.

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. This guidance is effective for annual and interim periods beginning after December 15, 2017. 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.

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. Management is evaluating the new guidance, but does not expect the adoption of this guidance will materially impact the Company's financial condition, results of operations, or liquidity.