Recent Developments, Including Mergers and Acquisitions	12 Months Ended
Dec. 31, 2017
Recent Developments Including Mergers And Acquisitions [Abstract]
Recent Developments, Including Mergers and Acquisitions	(2) RECENT DEVELOPMENTS, INCLUDING MERGERS AND ACQUISITIONS On January 12, 2018, the Company acquired First Wagoner Corp. and its subsidiary bank, First Bank & Trust Company and First Chandler Corp. and its subsidiary bank, First Bank of Chandler. See Note (24) for additional information on this subsequent event. On July 31, 2017, the Company completed a two-for-one stock split of the Company’s outstanding shares of common stock. The stock was payable in the form of a dividend on or about July 31, 2017 to shareholders of record of the outstanding common stock as of the close of business record date of July 17, 2017. Stockholders received one additional share for each share held on that date. This was the second stock split for the Company since going public. All share and per share amounts in these consolidated financial statements and related notes have been retroactively adjusted to reflect this stock split for all periods presented. Effective June 1, 2017, the Company organized a new captive insurance company named BancFirst Risk and Insurance Company (“the Captive”). The Captive is a wholly-owned subsidiary of BancFirst Corporation and is regulated by the Oklahoma Insurance Department. It insures certain risks of the Company and has entered into reinsurance agreements with a risk-sharing pool. On October 8, 2015, the Company completed its acquisition of CSB Bancshares Inc. and its subsidiary bank, Bank of Commerce, with locations in Yukon, Mustang and El Reno, Oklahoma. Bank of Commerce had approximately $196 million in total assets, $147 million in loans, $175 million in deposits and $22 million in equity capital. The acquisition was accounted for under the acquisition method and the Company acquired 100% of the voting interest. Bank of Commerce operated as a subsidiary of BancFirst Corporation until it was merged into BancFirst on November 13, 2015. As a result of the acquisition, the Company recorded a core deposit intangible of approximately $7.1 million and goodwill of approximately $9.4 million. The effect of this acquisition was included in the consolidated financial statements of the Company from the date of acquisition forward. The acquisition did not have a material effect on the Company’s consolidated financial statements. The acquisition of CSB Bancshares Inc. and its subsidiary bank, Bank of Commerce complements the Company’s community banking strategy by adding two communities to its banking network in Oklahoma.

(2) RECENT DEVELOPMENTS, INCLUDING MERGERS AND ACQUISITIONS

On January 12, 2018, the Company acquired First Wagoner Corp. and its subsidiary bank, First Bank & Trust Company and First Chandler Corp. and its subsidiary bank, First Bank of Chandler. See Note (24) for additional information on this subsequent event.

On July 31, 2017, the Company completed a two-for-one stock split of the Company’s outstanding shares of common stock. The stock was payable in the form of a dividend on or about July 31, 2017 to shareholders of record of the outstanding common stock as of the close of business record date of July 17, 2017. Stockholders received one additional share for each share held on that date. This was the second stock split for the Company since going public. All share and per share amounts in these consolidated financial statements and related notes have been retroactively adjusted to reflect this stock split for all periods presented.

Effective June 1, 2017, the Company organized a new captive insurance company named BancFirst Risk and Insurance Company (“the Captive”). The Captive is a wholly-owned subsidiary of BancFirst Corporation and is regulated by the Oklahoma Insurance Department. It insures certain risks of the Company and has entered into reinsurance agreements with a risk-sharing pool.

On October 8, 2015, the Company completed its acquisition of CSB Bancshares Inc. and its subsidiary bank, Bank of Commerce, with locations in Yukon, Mustang and El Reno, Oklahoma. Bank of Commerce had approximately $196 million in total assets, $147 million in loans, $175 million in deposits and $22 million in equity capital. The acquisition was accounted for under the acquisition method and the Company acquired 100% of the voting interest. Bank of Commerce operated as a subsidiary of BancFirst Corporation until it was merged into BancFirst on November 13, 2015. As a result of the acquisition, the Company recorded a core deposit intangible of approximately $7.1 million and goodwill of approximately $9.4 million. The effect of this acquisition was included in the consolidated financial statements of the Company from the date of acquisition forward. The acquisition did not have a material effect on the Company’s consolidated financial statements. The acquisition of CSB Bancshares Inc. and its subsidiary bank, Bank of Commerce complements the Company’s community banking strategy by adding two communities to its banking network in Oklahoma.