Business Combinations	3 Months Ended
Mar. 31, 2018
Business Combinations [Abstract]
Business Combinations	Note 2—Business Combinations Proposed Merger with FNB Bancorp On December 11, 2017, the Company and FNB Bancorp, a California corporation (“FNBB”), entered into an Agreement and Plan of Merger and Reorganization (the “Merger Agreement”) pursuant to which FNBB will be merged with and into the Company, with the Company as the surviving corporation (the “Merger”). Management expects the acquisition to close in the second quarter of 2018, subject to the satisfaction of customary closing conditions, including regulatory and shareholder approvals. The Merger Agreement provides that immediately after the Merger, FNBB’s bank subsidiary, First National Bank of Northern California (“First National Bank”), will merge with and into the Company’s bank subsidiary, Tri Counties Bank, with Tri Counties Bank as the surviving bank (the “Bank Merger”). The Merger and Bank Merger are collectively referred to as the “Proposed Transaction.” The Merger Agreement provides that each share of FNBB common stock issued and outstanding immediately prior to the effective time of the Merger will be canceled and converted into the right to receive 0.98 shares of the Company’s common stock (the “Exchange Ratio”), with cash paid in lieu of fractional shares of the Company’s common stock. Based on the closing price of the Company’s common stock of $41.64 on December 8, 2017, the consideration value was $40.81 per share of FNBB common stock or approximately $315.3 million in aggregate. The value of the merger consideration will fluctuate until closing based on the value of the Company’s stock and subject to a trading collar in certain circumstances. Upon consummation of the Merger, the shareholders of FNBB will own approximately 24% of the combined company. The Merger Agreement includes a trading collar that could result in termination of the Merger Agreement or a change to the Exchange Ratio. First, the Company can elect to terminate the Merger Agreement if both (i) the average share price of the Company’s common stock for the 20 day period up to and including the fifth day prior to the closing date (the “Average Closing Share Price”) is greater than $49.78, which equals 120% of the average share price of the Company’s stock for the 20 trading-day period up to and including December 8, 2017, which was $41.48 (the “Initial Price”) and (ii) the Company’s common stock outperforms the KBW Regional Banking Index by more than 20%, unless FNBB agrees that the Exchange Ratio will be reduced and fewer shares of the Company’s common stock will be issued to FNBB shareholders on a per share basis. Conversely, FNBB can terminate the Merger Agreement if both (i) the Average Closing Share Price is less than $33.18, which is equivalent to 80% of the Initial Price, and (ii) the Company’s common stock underperforms the KBW Regional Banking Index by more than 20%, unless the Company agrees that the Exchange Ratio will be increased and more shares of the Company common stock will be issued to FNBB shareholders on a per share basis. Upon consummation of the Merger, each outstanding and unexercised option to acquire shares of FNBB common stock held by FNBB’s employees and directors will be canceled and, in exchange, the holder of the option will be entitled to receive, whether or not the option is fully vested, a lump sum cash payment equal to the product of (1) the number of shares of FNBB common stock remaining under the option multiplied by (2) the Exchange Ratio multiplied by (3) the amount, if any, by which the Average Closing Share Price exceeds the exercise price of the option. The consummation of the Merger is subject to a number of conditions, which include: (i) the approval of the Merger Agreement by FNBB’s shareholders and the approval of the Merger Agreement and the issuance of shares of the Company common stock by the Company’s shareholders; (ii) as of the closing of the Merger, FNBB shall have tangible common equity of not less than $119.0 million, subject to credit for certain merger-related expenses and certain assumptions and adjustments that are set forth in the Merger Agreement; (iii) the receipt of all necessary regulatory approvals for the Proposed Transaction, without the imposition of conditions or requirements that the Company’s Board of Directors reasonably determines in good faith would, individually or in the aggregate, materially reduce the economic benefits of the Proposed Transaction; (iv) the absence of any regulation, judgment, decree, injunction or other order of a governmental authority which prohibits the consummation of the Proposed Transaction or which prohibits or makes illegal the consummation of the Proposed Transaction; (v) the effective registration of the shares of the Company’s Common Stock to be issued to FNBB’s shareholders with the Securities and Exchange Commission (the “SEC”) and the approval of such shares for listing on the Nasdaq Global Select Market; (vi) all representations and warranties made by the Company and FNBB in the Merger Agreement must remain true and correct, except for certain inaccuracies that would not have, or would not reasonably be expected to have, a material adverse effect; and (vii) the Company and FNBB must have performed their respective obligations under the Merger Agreement in all material respects. On March 21, 2018, the Company filed a registration statement on Form S-4 that included historical and pro forma information required in connection with the Merger. The registration statement on Form S-4 was subsequently amended on April 18, 2018.

Note 2—Business Combinations

Proposed Merger with FNB Bancorp

On December 11, 2017, the Company and FNB Bancorp, a California corporation (“FNBB”), entered into an Agreement and Plan of Merger and Reorganization (the “Merger Agreement”) pursuant to which FNBB will be merged with and into the Company, with the Company as the surviving corporation (the “Merger”). Management expects the acquisition to close in the second quarter of 2018, subject to the satisfaction of customary closing conditions, including regulatory and shareholder approvals. The Merger Agreement provides that immediately after the Merger, FNBB’s bank subsidiary, First National Bank of Northern California (“First National Bank”), will merge with and into the Company’s bank subsidiary, Tri Counties Bank, with Tri Counties Bank as the surviving bank (the “Bank Merger”). The Merger and Bank Merger are collectively referred to as the “Proposed Transaction.”

The Merger Agreement provides that each share of FNBB common stock issued and outstanding immediately prior to the effective time of the Merger will be canceled and converted into the right to receive 0.98 shares of the Company’s common stock (the “Exchange Ratio”), with cash paid in lieu of fractional shares of the Company’s common stock.

Based on the closing price of the Company’s common stock of $41.64 on December 8, 2017, the consideration value was $40.81 per share of FNBB common stock or approximately $315.3 million in aggregate. The value of the merger consideration will fluctuate until closing based on the value of the Company’s stock and subject to a trading collar in certain circumstances. Upon consummation of the Merger, the shareholders of FNBB will own approximately 24% of the combined company.

The Merger Agreement includes a trading collar that could result in termination of the Merger Agreement or a change to the Exchange Ratio. First, the Company can elect to terminate the Merger Agreement if both (i) the average share price of the Company’s common stock for the 20 day period up to and including the fifth day prior to the closing date (the “Average Closing Share Price”) is greater than $49.78, which equals 120% of the average share price of the Company’s stock for the 20 trading-day period up to and including December 8, 2017, which was $41.48 (the “Initial Price”) and (ii) the Company’s common stock outperforms the KBW Regional Banking Index by more than 20%, unless FNBB agrees that the Exchange Ratio will be reduced and fewer shares of the Company’s common stock will be issued to FNBB shareholders on a per share basis. Conversely, FNBB can terminate the Merger Agreement if both (i) the Average Closing Share Price is less than $33.18, which is equivalent to 80% of the Initial Price, and (ii) the Company’s common stock underperforms the KBW Regional Banking Index by more than 20%, unless the Company agrees that the Exchange Ratio will be increased and more shares of the Company common stock will be issued to FNBB shareholders on a per share basis.

Upon consummation of the Merger, each outstanding and unexercised option to acquire shares of FNBB common stock held by FNBB’s employees and directors will be canceled and, in exchange, the holder of the option will be entitled to receive, whether or not the option is fully vested, a lump sum cash payment equal to the product of (1) the number of shares of FNBB common stock remaining under the option multiplied by (2) the Exchange Ratio multiplied by (3) the amount, if any, by which the Average Closing Share Price exceeds the exercise price of the option.

The consummation of the Merger is subject to a number of conditions, which include: (i) the approval of the Merger Agreement by FNBB’s shareholders and the approval of the Merger Agreement and the issuance of shares of the Company common stock by the Company’s shareholders; (ii) as of the closing of the Merger, FNBB shall have tangible common equity of not less than $119.0 million, subject to credit for certain merger-related expenses and certain assumptions and adjustments that are set forth in the Merger Agreement; (iii) the receipt of all necessary regulatory approvals for the Proposed Transaction, without the imposition of conditions or requirements that the Company’s Board of Directors reasonably determines in good faith would, individually or in the aggregate, materially reduce the economic benefits of the Proposed Transaction; (iv) the absence of any regulation, judgment, decree, injunction or other order of a governmental authority which prohibits the consummation of the Proposed Transaction or which prohibits or makes illegal the consummation of the Proposed Transaction; (v) the effective registration of the shares of the Company’s Common Stock to be issued to FNBB’s shareholders with the Securities and Exchange Commission (the “SEC”) and the approval of such shares for listing on the Nasdaq Global Select Market; (vi) all representations and warranties made by the Company and FNBB in the Merger Agreement must remain true and correct, except for certain inaccuracies that would not have, or would not reasonably be expected to have, a material adverse effect; and (vii) the Company and FNBB must have performed their respective obligations under the Merger Agreement in all material respects.

On March 21, 2018, the Company filed a registration statement on Form S-4 that included historical and pro forma information required in connection with the Merger. The registration statement on Form S-4 was subsequently amended on April 18, 2018.