Basis of Presentation (Policies)	9 Months Ended
Basis of Presentation (Policies)	Sep. 30, 2019
Accounting Policies [Abstract]
General	General In the opinion of management, the accompanying unaudited consolidated financial statements contain all adjustments necessary to present fairly the consolidated balance sheets, statements of income, comprehensive income, changes in stockholders’ equity and cash flows of Nicolet Bankshares, Inc. (the “Company” or “Nicolet”) and its subsidiaries, for the periods presented, and all such adjustments are of a normal recurring nature. All material intercompany transactions and balances have been eliminated. The results of operations for the interim periods are not necessarily indicative of the results to be expected for the entire year. These interim consolidated financial statements have been prepared according to the rules and regulations of the Securities and Exchange Commission and, therefore, certain information and footnote disclosures normally presented in accordance with generally accepted accounting principles in the United States of America (“U.S. GAAP”) have been omitted or abbreviated. These consolidated financial statements should be read in conjunction with the Company’s audited consolidated financial statements and footnotes included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2018.
Critical Accounting Policies and Estimates	Critical Accounting Policies and Estimates Preparation of consolidated financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the amounts reported in the consolidated financial statements and accompanying disclosures. These estimates are based on management’s best knowledge of current events and actions the Company may undertake in the future. Estimates are used in accounting for, among other items, the allowance for loan losses, valuation of loans in acquisition transactions, useful lives for depreciation and amortization, fair value of financial instruments, other-than-temporary impairment calculations, valuation of deferred tax assets, uncertain income tax positions and contingencies. Estimates that are particularly susceptible to significant change for the Company include the determination of the allowance for loan losses, the determination and assessment of deferred tax assets and liabilities, and the valuation of loans acquired in acquisition transactions; therefore, these are critical accounting policies. Factors that may cause sensitivity to the aforementioned estimates include but are not limited to: external market factors such as market interest rates and employment rates, changes to operating policies and procedures, changes in applicable banking or tax regulations, and changes to deferred tax estimates. Actual results may ultimately differ from estimates, although management does not generally believe such differences would materially affect the consolidated financial statements in any individual reporting period presented. There have been no material changes or developments with respect to the assumptions or methodologies that the Company uses when applying what management believes are critical accounting policies and developing critical accounting estimates as disclosed in the Company’s Annual Report on Form 10-K for the year ended December 31, 2018.
Recent Accounting Developments Adopted	Recent Accounting Developments Adopted In August 2017, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update (“ASU”) 2017-12, Derivatives and Hedging (Topic 815): Targeted Improvements to Accounting for Hedging Activities. ASU 2017-12 expands the activities that qualify for hedge accounting and simplifies the rules for reporting hedging transactions. The updated guidance is effective for interim and annual reporting periods beginning after December 15, 2018, with early adoption permitted. The Company adopted the updated guidance effective January 1, 2019 with no material impact on its consolidated financial statements, because the Company does not have any significant derivatives and does not currently apply hedge accounting to derivatives. In February 2016, the FASB issued ASU 2016-02, Leases (Topic 842), with several subsequent updates. Topic 842 introduced a new accounting model for lessors and lessees. For lessees, almost all leases are now recognized on the balance sheet as a right-of-use ("ROU") asset and lease liability, unlike previous GAAP which required only capital leases to be recognized on the balance sheet. The accounting applied by lessors is largely unchanged from existing guidance. Topic 842 also requires additional disclosures concerning the amount, timing and uncertainty of cash flows arising from leases. The updated guidance is effective for annual reporting periods beginning after December 15, 2018, and provides a modified retrospective transition approach that allows lessees to recognize and measure leases on the balance sheet at the beginning of either the earliest period presented or as of the beginning of the period of adoption (the "effective date" method), with the option to elect certain practical expedients. Nicolet adopted the new guidance prospectively as of January 1, 2019, using the effective date method; thus, prior comparative periods have not been restated. Upon adoption, Nicolet recognized an ROU asset and lease liability of approximately $5 million. There was no impact to its consolidated statements of income or cash flows compared to the prior lease accounting model. The ROU asset and lease liability are recorded in other assets and other liabilities, respectively, in the consolidated balance sheets. As part of the adoption, Nicolet elected the package of practical expedients permitted under the transition guidance of the new standard which allowed the carry forward of the historical lease classification. Nicolet also elected the practical expedient to group lease and non-lease components as a single lease component; thus, the Company's leases include both lease (e.g., fixed payments including rent, taxes, and insurance costs) and non-lease components (e.g., common area or other maintenance costs). See Note 10 for the new disclosures required by Topic 842.
Reclassifications	Reclassifications Certain amounts in the 2018 consolidated financial statements have been reclassified to conform to the 2019 presentation.