Basis of Presentation and Significant Accounting Policies	9 Months Ended
Sep. 30, 2017
Accounting Policies [Abstract]
Basis of Presentation and Significant Accounting Policies	Basis of Presentation and Significant Accounting Policies Nature of Operations Chemical Financial Corporation ("Corporation" or "Chemical") operates in a single operating segment — commercial banking. The Corporation is a financial holding company, headquartered in Midland, Michigan, that operates through one commercial bank, Chemical Bank. Chemical Bank operates within Michigan, Ohio and Indiana as a Michigan state-chartered commercial bank. Chemical Bank operates through an internal organizational structure of seven regional banking units and offers a full range of traditional banking and fiduciary products and services to the residents and business customers in the bank’s geographical market areas. The products and services offered by the regional banking units, through branch banking offices, are generally consistent throughout the Corporation, as is the pricing of those products and services. The marketing of products and services throughout the Corporation’s regional banking units is generally uniform, as many of the markets served by the regional banking units overlap. The distribution of products and services is generally uniform throughout the Corporation’s regional banking units and is achieved primarily through retail branch banking offices, automated teller machines and electronically accessed banking products. The Corporation’s primary sources of revenue are interest from its loan products and investment securities, service charges and fees from customer deposit accounts, wealth management revenue and net gain on sale of loans and other mortgage banking revenue. Basis of Presentation and Principles of Consolidation The accompanying unaudited consolidated financial statements of the Corporation and its subsidiaries have been prepared in accordance with United States ("U.S.") generally accepted accounting principles ("GAAP") for interim financial information and with instructions to Form 10-Q and Rule 10-01 of Regulation S-X. Accordingly, the interim consolidated financial statements do not include all of the information and footnotes required by GAAP for complete financial statements and should be read in conjunction with the Corporation’s consolidated financial statements and footnotes thereto included in the Corporation’s Annual Report on Form 10-K for the year ended December 31, 2016. In the opinion of management, the accompanying unaudited interim consolidated financial statements contain all adjustments believed necessary to present fairly the financial condition and results of operations of the Corporation for the periods presented. Operating results for the nine months ended September 30, 2017 are not necessarily indicative of the results that may be expected for the year ending December 31, 2017. Use of Estimates Management makes estimates and assumptions that affect the amounts reported in the Consolidated Financial Statements and accompanying footnotes. Estimates that are particularly susceptible to significant change include the determination of the allowance for loan losses, expected cash flows from acquired loans, fair value amounts related to business combinations, income taxes, goodwill impairment and those assets and liabilities that require fair value measurement. Actual results could differ from these estimates. Recently Adopted Accounting Principles Stock Compensation In March 2016, the FASB issued ASU No. 2016-09, Compensation - Stock Compensation (Topic 718): Improvements to Employee Share-Based Payment Accounting ("ASU 2016-09"), which simplifies the accounting for employee share-based payment transactions including the accounting for income taxes, forfeitures and statutory holding requirements, as well as classification on the statement of cash flows. ASU 2016-09 is effective for public companies for interim and annual periods beginning after December 15, 2016 with early adoption permitted for any interim or annual period. If an entity early adopts the amendments, any adjustment should be reflected as of the beginning of the fiscal year. The Corporation elected to early adopt ASU 2016-09 during the fourth quarter of 2016. All quarters during the year ended December 31, 2016 have been adjusted as a result of this adoption. Prior to adoption of ASU 2016-09, all excess tax benefits resulting from the exercise or settlement of share-based payment transactions were recognized in additional-paid-in-capital ("APIC") and accumulated in an APIC pool, while tax deficiencies were either offset against the APIC pool or recognized in the income statement if no APIC pool was available. The new guidance eliminates additions to the APIC pool and all excess tax benefits and deficiencies are recognized as an income tax benefit or expense in the income statement prospectively. Accordingly, periods prior to January 1, 2016 have not been adjusted. During the year ended December 31, 2016, $2.2 million of excess tax benefits were recognized as income tax benefit. Loan Servicing Rights Effective January 1, 2017, the Corporation elected to account for all loan servicing rights ("LSRs") previously accounted for under the lower of cost or fair value method under the fair value method. The guidance in Accounting Standards Codification Subtopic 860-50, "Transfers and Servicing-Servicing Assets and Liabilities" provides that an entity may make an irrevocable decision to subsequently measure a class of servicing assets and servicing liabilities at fair value at the beginning of any fiscal year. The guidance allows for the Corporation to apply this election prospectively to all new and existing servicing assets and servicing liabilities. Management believes this election will provide more comparable results to peers as many of those within our industry group account for loan servicing rights under the fair value method. The change in accounting policy in the first quarter of 2017 resulted in a cumulative adjustment to increase retained earnings in the amount of $3.7 million, net of taxes. Investment Securities The Corporation elected to early adopt Accounting Standards Update ("ASU") No. 2017-08, Receivables-Nonrefundable Fees and Other Costs (Subtopic 310-20): Premium Amortization on Purchased Callable Debt Securities ("ASU 2017-08") during the second quarter of 2017. The guidance in ASU 2017-08 shortens the amortization period for certain callable debt securities that are held at a premium to the earliest call date. Debt securities held at a discount will continue to be amortized as a yield adjustment over the life of the instrument. The early adoption of ASU 2017-08 in the second quarter of 2017 did not have a material impact on the consolidated financial statements.

Basis of Presentation and Significant Accounting Policies

Nature of Operations

Chemical Financial Corporation ("Corporation" or "Chemical") operates in a single operating segment — commercial banking. The Corporation is a financial holding company, headquartered in Midland, Michigan, that operates through one commercial bank, Chemical Bank. Chemical Bank operates within Michigan, Ohio and Indiana as a Michigan state-chartered commercial bank. Chemical Bank operates through an internal organizational structure of seven regional banking units and offers a full range of traditional banking and fiduciary products and services to the residents and business customers in the bank’s geographical market areas. The products and services offered by the regional banking units, through branch banking offices, are generally consistent throughout the Corporation, as is the pricing of those products and services. The marketing of products and services throughout the Corporation’s regional banking units is generally uniform, as many of the markets served by the regional banking units overlap. The distribution of products and services is generally uniform throughout the Corporation’s regional banking units and is achieved primarily through retail branch banking offices, automated teller machines and electronically accessed banking products.

The Corporation’s primary sources of revenue are interest from its loan products and investment securities, service charges and fees from customer deposit accounts, wealth management revenue and net gain on sale of loans and other mortgage banking revenue.

Basis of Presentation and Principles of Consolidation

The accompanying unaudited consolidated financial statements of the Corporation and its subsidiaries have been prepared in accordance with United States ("U.S.") generally accepted accounting principles ("GAAP") for interim financial information and with instructions to Form 10-Q and Rule 10-01 of Regulation S-X. Accordingly, the interim consolidated financial statements do not include all of the information and footnotes required by GAAP for complete financial statements and should be read in conjunction with the Corporation’s consolidated financial statements and footnotes thereto included in the Corporation’s Annual Report on Form 10-K for the year ended December 31, 2016. In the opinion of management, the accompanying unaudited interim consolidated financial statements contain all adjustments believed necessary to present fairly the financial condition and results of operations of the Corporation for the periods presented. Operating results for the nine months ended September 30, 2017 are not necessarily indicative of the results that may be expected for the year ending December 31, 2017.

Use of Estimates

Management makes estimates and assumptions that affect the amounts reported in the Consolidated Financial Statements and accompanying footnotes. Estimates that are particularly susceptible to significant change include the determination of the allowance for loan losses, expected cash flows from acquired loans, fair value amounts related to business combinations, income taxes, goodwill impairment and those assets and liabilities that require fair value measurement. Actual results could differ from these estimates.

Recently Adopted Accounting Principles

Stock Compensation

In March 2016, the FASB issued ASU No. 2016-09, Compensation - Stock Compensation (Topic 718): Improvements to Employee Share-Based Payment Accounting ("ASU 2016-09"), which simplifies the accounting for employee share-based payment transactions including the accounting for income taxes, forfeitures and statutory holding requirements, as well as classification on the statement of cash flows. ASU 2016-09 is effective for public companies for interim and annual periods beginning after December 15, 2016 with early adoption permitted for any interim or annual period. If an entity early adopts the amendments, any adjustment should be reflected as of the beginning of the fiscal year. The Corporation elected to early adopt ASU 2016-09 during the fourth quarter of 2016. All quarters during the year ended December 31, 2016 have been adjusted as a result of this adoption.

Prior to adoption of ASU 2016-09, all excess tax benefits resulting from the exercise or settlement of share-based payment transactions were recognized in additional-paid-in-capital ("APIC") and accumulated in an APIC pool, while tax deficiencies were either offset against the APIC pool or recognized in the income statement if no APIC pool was available. The new guidance eliminates additions to the APIC pool and all excess tax benefits and deficiencies are recognized as an income tax benefit or expense in the income statement prospectively. Accordingly, periods prior to January 1, 2016 have not been adjusted. During the year ended December 31, 2016, $2.2 million of excess tax benefits were recognized as income tax benefit.

Loan Servicing Rights

Effective January 1, 2017, the Corporation elected to account for all loan servicing rights ("LSRs") previously accounted for under the lower of cost or fair value method under the fair value method. The guidance in Accounting Standards Codification Subtopic 860-50, "Transfers and Servicing-Servicing Assets and Liabilities" provides that an entity may make an irrevocable decision to subsequently measure a class of servicing assets and servicing liabilities at fair value at the beginning of any fiscal year. The guidance allows for the Corporation to apply this election prospectively to all new and existing servicing assets and servicing liabilities. Management believes this election will provide more comparable results to peers as many of those within our industry group account for loan servicing rights under the fair value method. The change in accounting policy in the first quarter of 2017 resulted in a cumulative adjustment to increase retained earnings in the amount of $3.7 million, net of taxes.

Investment Securities

The Corporation elected to early adopt Accounting Standards Update ("ASU") No. 2017-08, Receivables-Nonrefundable Fees and Other Costs (Subtopic 310-20): Premium Amortization on Purchased Callable Debt Securities ("ASU 2017-08") during the second quarter of 2017. The guidance in ASU 2017-08 shortens the amortization period for certain callable debt securities that are held at a premium to the earliest call date. Debt securities held at a discount will continue to be amortized as a yield adjustment over the life of the instrument. The early adoption of ASU 2017-08 in the second quarter of 2017 did not have a material impact on the consolidated financial statements.