Summary of Significant Accounting Policies (Policies)	6 Months Ended
Summary of Significant Accounting Policies (Policies)	Jun. 30, 2019
Accounting Policies [Abstract]
Description of Business and Basis of Presentation	Description of Business and Basis of Presentation TriCo Bancshares (the “Company” or “we”) is a California corporation organized to act as a bank holding company for Tri Counties Bank (the “Bank”). The Company and the Bank are headquartered in Chico, California. The Bank is a California-chartered bank that is engaged in the general commercial banking business in 29 California counties. The Company has five capital subsidiary business trusts (collectively, the “Capital Trusts”) that issued trust preferred securities, including two organized by the Company and three acquired with the acquisition of North Valley Bancorp. The consolidated financial statements are prepared in accordance with accounting policies generally accepted in the United States of America and general practices in the banking industry. All adjustments necessary for a fair presentation of these consolidated financial statements have been included and are of a normal and recurring nature. The financial statements include the accounts of the Company. All inter-company accounts and transactions have been eliminated in consolidation. For financial reporting purposes, the Company’s investments in the Capital Trusts of $1,716,000 are accounted for under the equity method and, accordingly, are not consolidated and are included in other assets on the consolidated balance sheet. The subordinated debentures issued and guaranteed by the Company and held by the Capital Trusts are reflected as debt on the Company’s consolidated balance sheet.
Use of Estimates in the Preparation of Financial Statements	Use of Estimates in the Preparation of Financial Statements The preparation of financial statements in conformity with accounting principles generally accepted in the United States of America requires Management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of revenues and expenses during the reporting period. The Company bases its estimates on historical experience and on various other assumptions that are believed to be reasonable under the circumstances, the results of which form the basis for making judgments about the carrying values of assets and liabilities that are not readily apparent from other sources. Actual results may differ from these estimates under different assumptions or conditions. Certain information and footnote disclosures normally included in financial statements prepared in accordance with accounting principles generally accepted in the United States of America have been condensed or omitted pursuant to the rules and regulations of the Securities and Exchange Commission. These unaudited condensed consolidated financial statements should be read in conjunction with the audited consolidtated financial statements and notes thereto included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2018 (the “2018 Annual Report”). The Company believes that the disclosures made are adequate to make the inforamtion not misleading.
Segment and Significant Group Concentration of Credit Risk	Segment and Significant Group Concentration of Credit Risk The Company grants agribusiness, commercial, consumer, and residential loans to customers located throughout northern and central California. The Company has a diversified loan portfolio within the business segments located in this geographical area. The Company currently classifies all its operation into one business segment that it denotes as community banking.
Geographical Descriptions	Geographical Descriptions For the purpose of describing the geographical location of the Company’s operations, the Company has defined northern California as that area of California north of, and including, Stockton to the east and San Jose to the west; central California as that area of the state south of Stockton and San Jose, to and including, Bakersfield to the east and San Luis Obispo to the west; and southern California as that area of the state south of Bakersfield and San Luis Obispo.
Cash and Cash Equivalents	Cash and Cash Equivalents Net cash flows are reported for loan and deposit transactions and other borrowings. For purposes of the consolidated statement of cash flows, cash, due from banks with original maturities less than 90 days, interest-earning deposits in other banks, and Federal funds sold are considered to be cash equivalents.
Accounting Standards Adopted in 2019	Accounting Standards Adopted in 2019 The Financial Accounting Standards Board (“FASB”) issued ASU No. 2016-02, Leases (Topic 842) . ASU 2016-02, which among other things, requires lessees to recognize most leases on-balance sheet, increasing reported assets and liabilities. Lessor accounting remains substantially similar to current U.S. GAAP. The FASB has issued incremental guidance to Topic 842 standard through ASU No. 2018-11, 2018-20, and 2019-01. The Company has elected to use the transition relief approach as provided in ASU 2018-11, which permits the Company to use January 1, 2019 as both the application date and the adoption date, rather than the modified retrospective approach which would have required an application date of January 1, 2017 and adoption date of January 1, 2019. The Company also elected certain relief options offered within the new standard, which include the package of practical expedients, the option not to recognize a right-of-use asset (ROUA) and lease liability that arise from short-term leases (i.e. leases with terms of 12 months or less), and the option of hindsight when determining lease term. Substantially all of the Company’s lease agreements are considered operating leases and were not previously recognized on the Company’s balance sheets. As of January 1, 2019, the Company recorded a ROUA and corresponding lease liability for all applicable operating leases. While the guidance increased the Company’s gross assets and liabilities, the adoption of ASU 2016-02 did not have a material impact on the consolidated statements of income or the consolidated statements of cash flows. See Note 6 for more information. The FASB issued ASU 2017-08, Receivables - Nonrefundable Fees and Other Costs (Topic 310). ASU 2017-08 shortens the amortization period for certain callable debt securities held at a premium to require such premiums to be amortized to the earliest call date unless applicable guidance related to certain pools of securities is applied to consider estimated prepayments. Under prior guidance, entities were generally required to amortize premiums on individual, non-pooled callable debt securities as a yield adjustment over the contractual life of the security. ASU 2017-08 does not change the accounting for callable debt securities held at a discount. ASU 2017-08 was effective for the Company on January 1, 2019, and did not have an impact on the Company’s consolidated financial statements.
Accounting Standards Pending Adoption	Accounting Standards Pending Adoption The FASB issued ASU No. 2016-13, Financial Instruments – Credit Losses (Topic 326) . ASU 2016-13 is the final guidance on the new current expected credit loss (‘‘CECL’’) model. ASU 2016-13, among other things, requires the incurred loss impairment methodology in current GAAP be replaced with a methodology that reflects expected credit losses and requires consideration of a broader range of reasonable and supportable information to estimate future credit loss estimates. As CECL encompasses all financial assets carried at amortized cost, the requirement that reserves be established based on an organization’s reasonable and supportable estimate of expected credit losses extends to held to maturity (‘‘HTM’’) debt securities. ASU 2016-13 amends the accounting for credit losses on available-for-sale securities (‘‘AFS’’), whereby credit losses will be presented as an allowance as opposed to a write-down. In addition, CECL will modify the accounting for purchased loans with credit deterioration since origination, so that reserves are established at the date of acquisition for purchased loans. Lastly, ASU 2016-13 requires enhanced disclosures on the significant estimates and judgments used to estimate credit losses, as well as on the credit quality and underwriting standards of an organization’s portfolio. These disclosures require organizations to present the currently required credit quality disclosures disaggregated by the year of origination or vintage. ASU 2016-13 allows for a modified retrospective approach with a cumulative effect adjustment to the balance sheet upon adoption (charge to retained earnings instead of the income statement). ASU 2016-13 will be effective for the Company on January 1, 2020, and early adoption is permitted. While the Company is currently evaluating the provisions of ASU 2016-13 to determine the potential impact the new standard will have on the Company’s consolidated financial statements, it has taken steps to prepare for the implementation when it becomes effective, such as forming an internal task force, gathering pertinent data, consulting with outside professionals, and evaluating its current IT systems. While detailed modeling efforts are ongoing, the validation of expected credit loss estimates will likely not be available until late in 2019. Management expects to recognize a one-time cumulative effect adjustment to the allowance for loan losses as of the first reporting period in which the new standard is effective, but cannot yet estimate the magnitude of the one-time adjustment or the overall impact of the new guidance on the Company’s financial position, results of operations or cash flows. FASB issued ASU No. 2017-04, Intangibles—Goodwill and Other: Simplifying the Test for Goodwill Impairment (Topic 350): ASU 2017-04 eliminates step two of the goodwill impairment test (the hypothetical purchase price allocation used to determine the implied fair value of goodwill) when step one (determining if the carrying value of a reporting unit exceeds its fair value) is failed. Instead, entities simply will compare the fair value of a reporting unit to its carrying amount and record goodwill impairment for the amount by which the reporting unit’s carrying amount exceeds its fair value. ASU 2017-04 will be effective for the Company on January 1, 2020 and is not expected to have a significant impact on the Company’s consolidated financial statements. In August 2018, the FASB issued ASU No. 2018-13, “Disclosure Framework - Changes to the Disclosure Requirements for Fair Value Measurement.” This ASU eliminates, adds and modifies certain disclosure requirements for fair value measurements. Among the changes, entities will no longer be required to disclose the amount of and reasons for transfers between Level 1 and Level 2 of the fair value hierarchy, but will be required to disclose the range and weighted average used to develop significant unobservable inputs for Level 3 fair value measurements. ASU No. 2018-13 is effective for interim and annual reporting periods beginning after December 15, 2019; early adoption is permitted. Entities are also allowed to elect early adoption the eliminated or modified disclosure requirements and delay adoption of the new disclosure requirements until their effective date. As ASU No. 2018-13 only revises disclosure requirements, it will not have a significant impact on the Company’s consolidated financial statements. In August 2018, the FASB issued ASU No. 2018-14, “Disclosure Framework - Changes to the Disclosure Requirements for Defined Benefit Plans .” This ASU makes minor changes to the disclosure requirements for employers that sponsor defined benefit pension and/or other postretirement benefit plans. ASU 2018-14 is effective for fiscal years ending after December 15, 2020; early adoption is permitted. As ASU 2018-14 only revises disclosure requirements, it will not have a significant impact on the Company’s consolidated financial statements.