Description of Business and Summary of Significant Accounting Policies (Policies)	6 Months Ended
Jun. 30, 2019
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The accompanying unaudited interim consolidated financial statements include the accounts of BancFirst Corporation, Council Oak Partners, LLC, BancFirst Insurance Services, Inc., BancFirst Risk & Insurance Company and BancFirst and its subsidiaries. The principal operating subsidiaries of BancFirst are Council Oak Investment Corporation, Council Oak Real Estate, Inc., BFTower, LLC and BancFirst Agency, Inc. All significant intercompany accounts and transactions have been eliminated. Assets held in a fiduciary or agency capacity are not assets of the Company and, accordingly, are not included in the unaudited interim consolidated financial statements. The accompanying unaudited interim consolidated financial statements and notes are presented in accordance with the instructions for Form 10-Q. The information contained in the financial statements and footnotes included in BancFirst Corporation’s Annual Report on Form 10-K for the year ended December 31, 2018, should be referred to in connection with these unaudited interim consolidated financial statements. Operating results for the interim periods disclosed herein are not necessarily indicative of the results that may be expected for a full year or any future period. The unaudited interim consolidated financial statements contained herein reflect all adjustments which are, in the opinion of management, necessary to provide a fair statement of the financial position and results of operations of the Company for the interim periods presented. All such adjustments are of a normal and recurring nature. There have been no significant changes in the accounting policies of the Company since December 31, 2018, the date of the most recent annual report.
Reclassifications	Reclassifications Certain items in prior financial statements have been reclassified to conform to the current presentation. Such reclassifications had no effect on previously reported net cash flows, stockholders’ equity or comprehensive income.
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 inherently involves the use of estimates and assumptions that affect the amounts reported in the financial statements and the related disclosures. These estimates relate principally to the determination of the allowance for loan losses, income taxes, the fair value of financial instruments and the valuation of intangibles. Such estimates and assumptions may change over time and actual amounts realized may differ from those reported.
Recent Accounting Pronouncements	Recent Accounting Pronouncements Standards Adopted During Current Period: In February 2016, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update (“ASU”) No. 2016-02, “Leases - (Topic 842)”, amended by ASU 2018-11, “Leases – (Topic 842)”: Targeted Improvements. This new guidance requires a lessee to recognize on the balance sheet the assets and liabilities for the rights and obligations created by leases with lease terms of more than twelve months and provide additional disclosures. The amendments were effective for annual periods, and interim reporting periods within those annual periods, beginning after December 15, 2018. The Company adopted this new standard on January 1, 2019, using a modified retrospective transition approach and recognized right-of-use lease assets and related lease liabilities totaling $4.3 million. The Company elected to apply certain practical adoption expedients provided under the updates whereby it did not reassess initial direct costs for any existing leases. No cumulative-effect adjustment was recognized as the amount was not material, and the impact on our results of operations and cash flows was also not material. No prior periods were adjusted. See Note 6 for the financial position impact and additional disclosures. Standards Not Yet Adopted: In August 2018, the FASB issued ASU No. 2018-13, “Fair Value Measurement (Topic 820).” ASU 2018-13 removes, modifies and adds disclosure requirements on fair value measurements. ASU 2018-13 will be effective for the Company on January 1, 2020. Early adoption is permitted. In addition, early adoption of any removed or modified disclosures and delayed adoption of the additional disclosures until the effective date is also permitted. The Company expects to adopt the standard in the first quarter of 2020. In June 2016, the FASB issued ASU No. 2016-13, “Financial Instruments – Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments.” ASU 2016-13 requires a financial asset measured at amortized cost basis to be presented at the net amount expected to be collected. The measurement of expected credit losses is based on relevant information about past events, including historical experience, current conditions, and reasonable and supportable forecasts that affect the collectability of the reported amount. ASU 2016-13 requires enhanced disclosures related to the significant estimates and judgements used in estimating credit losses, as well as the credit quality and underwriting standards of an organization’s portfolio. In addition, ASU 2016-13 amends the accounting for credit losses on available-for-sale debt securities and purchased financial assets with credit deterioration. ASU 2016-13 will be effective for the Company on January 1, 2020. The Company is currently evaluating the potential impact of ASU 2016-13 on its financial statements. In that regard, the Company has formed a task force under the direction of its Chief Financial Officer. In preparation, the Company has developed new credit estimation models, processes and controls. Internal validation of the model is underway and expected to be completed during the third quarter of 2019. The Company has performed test runs of the new processes and controls and will begin full parallel runs next quarter. The adoption of ASU 2016-13 could result in an increase or decrease in the allowance for loan losses as a result of changing from an “incurred loss” model, which encompasses allowances for current known and inherent losses within the portfolio, to an “expected loss” model, which encompasses allowances for losses expected to be incurred over the life of the portfolio. Furthermore, ASU 2016-13 will necessitate that the Company establish an allowance for expected credit losses for certain debt securities and other financial assets. While the Company is currently unable to reasonably estimate the impact of adopting ASU 2016-13, we expect that the impact of adoption will be significantly influenced by the composition, characteristics and quality of our loan and securities portfolios as well as the prevailing economic conditions and forecasts as of the adoption date. The Company expects to adopt the standard in the first quarter of 2020.

Description of Business and Summary of Significant Accounting Policies (Policies)

6 Months Ended

Jun. 30, 2019

The accompanying unaudited interim consolidated financial statements include the accounts of BancFirst Corporation, Council Oak Partners, LLC, BancFirst Insurance Services, Inc., BancFirst Risk & Insurance Company and BancFirst and its subsidiaries. The principal operating subsidiaries of BancFirst are Council Oak Investment Corporation, Council Oak Real Estate, Inc., BFTower, LLC and BancFirst Agency, Inc. All significant intercompany accounts and transactions have been eliminated. Assets held in a fiduciary or agency capacity are not assets of the Company and, accordingly, are not included in the unaudited interim consolidated financial statements.

The accompanying unaudited interim consolidated financial statements and notes are presented in accordance with the instructions for Form 10-Q. The information contained in the financial statements and footnotes included in BancFirst Corporation’s Annual Report on Form 10-K for the year ended December 31, 2018, should be referred to in connection with these unaudited interim consolidated financial statements. Operating results for the interim periods disclosed herein are not necessarily indicative of the results that may be expected for a full year or any future period.

The unaudited interim consolidated financial statements contained herein reflect all adjustments which are, in the opinion of management, necessary to provide a fair statement of the financial position and results of operations of the Company for the interim periods presented. All such adjustments are of a normal and recurring nature. There have been no significant changes in the accounting policies of the Company since December 31, 2018, the date of the most recent annual report.

Reclassifications

Certain items in prior financial statements have been reclassified to conform to the current presentation. Such reclassifications had no effect on previously reported net cash flows, stockholders’ equity or comprehensive income.

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 inherently involves the use of estimates and assumptions that affect the amounts reported in the financial statements and the related disclosures. These estimates relate principally to the determination of the allowance for loan losses, income taxes, the fair value of financial instruments and the valuation of intangibles. Such estimates and assumptions may change over time and actual amounts realized may differ from those reported.

Recent Accounting Pronouncements

Standards Adopted During Current Period:

In February 2016, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update (“ASU”) No. 2016-02, “Leases - (Topic 842)”, amended by ASU 2018-11, “Leases – (Topic 842)”: Targeted Improvements. This new guidance requires a lessee to recognize on the balance sheet the assets and liabilities for the rights and obligations created by leases with lease terms of more than twelve months and provide additional disclosures. The amendments were effective for annual periods, and interim reporting periods within those annual periods, beginning after December 15, 2018. The Company adopted this new standard on January 1, 2019, using a modified retrospective transition approach and recognized right-of-use lease assets and related lease liabilities totaling $4.3 million. The Company elected to apply certain practical adoption expedients provided under the updates whereby it did not reassess initial direct costs for any existing leases. No cumulative-effect adjustment was recognized as the amount was not material, and the impact on our results of operations and cash flows was also not material. No prior periods were adjusted. See Note 6 for the financial position impact and additional disclosures.

Standards Not Yet Adopted:

In August 2018, the FASB issued ASU No. 2018-13, “Fair Value Measurement (Topic 820).” ASU 2018-13 removes, modifies and adds disclosure requirements on fair value measurements. ASU 2018-13 will be effective for the Company on January 1, 2020. Early adoption is permitted. In addition, early adoption of any removed or modified disclosures and delayed adoption of the additional disclosures until the effective date is also permitted. The Company expects to adopt the standard in the first quarter of 2020.

In June 2016, the FASB issued ASU No. 2016-13, “Financial Instruments – Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments.” ASU 2016-13 requires a financial asset measured at amortized cost basis to be presented at the net amount expected to be collected. The measurement of expected credit losses is based on relevant information about past events, including historical experience, current conditions, and reasonable and supportable forecasts that affect the collectability of the reported amount. ASU 2016-13 requires enhanced disclosures related to the significant estimates and judgements used in estimating credit losses, as well as the credit quality and underwriting standards of an organization’s portfolio. In addition, ASU 2016-13 amends the accounting for credit losses on available-for-sale debt securities and purchased financial assets with credit deterioration. ASU 2016-13 will be effective for the Company on January 1, 2020. The Company is currently evaluating the potential impact of ASU 2016-13 on its financial statements. In that regard, the Company has formed a task force under the direction of its Chief Financial Officer. In preparation, the Company has developed new credit estimation models, processes and controls. Internal validation of the model is underway and expected to be completed during the third quarter of 2019. The Company has performed test runs of the new processes and controls and will begin full parallel runs next quarter. The adoption of ASU 2016-13 could result in an increase or decrease in the allowance for loan losses as a result of changing from an “incurred loss” model, which encompasses allowances for current known and inherent losses within the portfolio, to an “expected loss” model, which encompasses allowances for losses expected to be incurred over the life of the portfolio. Furthermore, ASU 2016-13 will necessitate that the Company establish an allowance for expected credit losses for certain debt securities and other financial assets. While the Company is currently unable to reasonably estimate the impact of adopting ASU 2016-13, we expect that the impact of adoption will be significantly influenced by the composition, characteristics and quality of our loan and securities portfolios as well as the prevailing economic conditions and forecasts as of the adoption date. The Company expects to adopt the standard in the first quarter of 2020.