Employee benefit plans	12 Months Ended
Dec. 31, 2018
Retirement Benefits [Abstract]
Employee benefit plans	Employee benefit plans: (A)—401(k) plan: The Bank has a 401(k) Plan (the “Plan”) whereby substantially all employees participate in the Plan. Employees may contribute the maximum amount of their eligible compensation subject to certain limits based on the federal tax laws. The Bank makes matching contributions of 25% of participant contributions not to exceed 6% of an employee’s total compensation. The Bank may also make discretionary Profit Sharing contributions. Matching and profit sharing contributions are vested equally over five years. For the years ended December 31, 2018, 2017 and 2016, the matching portions provided by the Bank to this Plan were $2,211 and $2,344 and $1,379 respectively, which includes the additional discretionary contribution of 25% match contributed in those years. (B)—Acquired supplemental retirement plans: In prior years, the Company assumed certain nonqualified supplemental retirement plans for certain former employees of acquired entities. At December 31, 2018 and 2017, other liabilities on the consolidated balance sheet include post-retirement benefits payable of $1,260 and $1,510, respectively, related to these plans. For the years ended December 31, 2018, 2017 and 2016, the Company recorded expense of $4, $4 and $30, respectively, related to these plans and payments to the participants were $191, $191 and $205 in 2018, 2017 and 2016, respectively. The Company also acquired single premium life insurance policies on these individuals. At December 31, 2018 and 2017, other assets on the consolidated balance sheet include $11,115 and $10,873 and reported cash value income (net of related insurance premium expense) of $158, $164 and $181 in 2018, 2017 and 2016, respectively. (C)—Deferred compensation plans and agreements: The Bank granted awards (“EBI Units”) to certain employees pursuant to the FirstBank 2010 Equity Based Incentive Plan (the “2010 EBI Plan”), the FirstBank 2012 Equity Based Incentive Plan (the “2012 EBI Plan”) and the FirstBank Preferred Equity Based Incentive Plan (the “Preferred EBI Plan” and, together with the 2010 EBI Plan and the 2012 EBI Plan, the “EBI Plans”). Prior to the initial public offering, awards granted under EBI Plans were settled in cash only. Following the initial public offering, participants in the EBI Plans were given the one-time option to elect, for each EBI Unit vested to such participant, either (i) an amount in cash or (ii) a number of shares of Company common stock determined pursuant to a conversion formula that took into account the effect of the initial public offering. Consistent with the terms of the EBI Plans and approved by the Board of Directors, outstanding EBI Units were adjusted to reflect the 100-for-one stock split that was effectuated prior to the IPO. The Bank also has a separate deferred compensation agreement with one key executive. Each plan or agreement is an unfunded general obligation of the Bank. The plans and agreements have varying vesting periods and other terms as follows: 2010 EBI Plan— Pursuant to the terms of the 2010 EBI Plan, each EBI Unit vests ratably over five years, or earlier upon a change of control, death or disability or retirement after age 65. On or shortly following the vesting date, the holder of an EBI Unit will receive an amount in cash (or, if so elected by the participant following the IPO, in stock) equal to the fair market value of a share of common stock on the December 31 immediately preceding the payment date. Prior to the IPO, fair market value was determined by dividing 7.5% of the total assets of the Bank by the total number of outstanding common stock shares of the Company. Following the IPO, EBI Units are valued based upon the Company’s stock price. Units under this plan became fully vested January, 2017. Preferred EBI Plan—The Preferred EBI Plan has the same terms and conditions as those described above for the 2010 EBI Plan, with the exception of a seven year ratable vesting period. Units under this plan became fully vested January, 2017. 2012 EBI Plan— Pursuant to the terms of the 2012 EBI Plan, each EBI Unit vests and becomes payable following the third anniversary of the date of grant, or earlier upon a change of control, death or disability or retirement after age 65. On or shortly following the vesting date, the holder of an EBI Unit will receive an amount in cash (or, if so elected by the participant following the IPO, in stock) equal to the fair market value of a share of common stock on the December 31 immediately preceding the payment date. Following the IPO, EBI Units are valued based upon the Company’s stock price. Prior to the IPO, fair market value of the Company was determined based upon the average of the sum of (a) 15 times the Company’s after-tax earnings, based on a default tax rate imposed by the Code, and (b) 1.5 times the Company’s tangible book value, defined as the consolidated equity of the Company less unrealized gains (losses) and less goodwill and intangible assets. Following the IPO, EBI Units outstanding under the 2012 EBI Plan were adjusted to prevent dilution of these EBI Units as a result of the IPO pursuant to the following conversion formula: (i) the number of EBI Units outstanding under the 2012 EBI Plan (as adjusted for the stock split), multiplied by (ii) 1.13 (determined by dividing $21.4085, the fair market value per EBI Unit as determined under the 2012 EBI Plan, by $19.00, the IPO price). Deferred compensation Agreement—Effective December 31, 2014, the Bank entered into an agreement with the Bank’s Chief Executive Officer to reward his prior service, pursuant to which he is entitled to receive a fixed lump sum cash payment equal to $3,000,000 on December 31, 2019 or the earlier occurrence of his separation of service or a change in control of the Company. On August 19, 2016, the Bank entered into an amendment to the deferred compensation agreement, pursuant to which the deferred account is now denominated in 157,895 deferred stock units, determined by dividing $3,000,000 by $19.00 (the IPO price). The deferred stock units are convertible on a 1-for-1 basis into shares of Company common stock on the original payment date described above. Summary—At December 31, 2018 and 2017, the accompanying consolidated balance sheet include liabilities for cash-settled awards under the EBI Plans amounted to $993 and $2,346, respectively. As of December 31, 2018 and 2017, there were 29,172 and 67,470 units, respectively, in the equity based incentive plan for those employees who elected cash settlement of EBI units. Subsequent to December 31, 2018, these cash-settled awards were fully distributed. For the year ended December 31, 2018 and 2017, the Company incurred expenses related to these plans and agreements totaling $3,787 and $3,685, respectively, which is included in salaries, commissions and employee benefits in the accompanying statement of income. Additionally, payments under the plans totaled $1,818 and $5,163, respectively, for 2018 and 2017.

Employee benefit plans:

(A)—401(k) plan:

The Bank has a 401(k) Plan (the “Plan”) whereby substantially all employees participate in the Plan. Employees may contribute the maximum amount of their eligible compensation subject to certain limits based on the federal tax laws. The Bank makes matching contributions of 25% of participant contributions not to exceed 6% of an employee’s total compensation. The Bank may also make discretionary Profit Sharing contributions. Matching and profit sharing contributions are vested equally over five years. For the years ended December 31, 2018, 2017 and 2016, the matching portions provided by the Bank to this Plan were $2,211 and $2,344 and $1,379 respectively, which includes the additional discretionary contribution of 25% match contributed in those years.

(B)—Acquired supplemental retirement plans:

In prior years, the Company assumed certain nonqualified supplemental retirement plans for certain former employees of acquired entities. At December 31, 2018 and 2017, other liabilities on the consolidated balance sheet include post-retirement benefits payable of $1,260 and $1,510, respectively, related to these plans. For the years ended December 31, 2018, 2017 and 2016, the Company recorded expense of $4, $4 and $30, respectively, related to these plans and payments to the participants were $191, $191 and $205 in 2018, 2017 and 2016, respectively. The Company also acquired single premium life insurance policies on these individuals. At December 31, 2018 and 2017, other assets on the consolidated balance sheet include $11,115 and $10,873 and reported cash value income (net of related insurance premium expense) of $158, $164 and $181 in 2018, 2017 and 2016, respectively.

(C)—Deferred compensation plans and agreements:

The Bank granted awards (“EBI Units”) to certain employees pursuant to the FirstBank 2010 Equity Based Incentive Plan (the “2010 EBI Plan”), the FirstBank 2012 Equity Based Incentive Plan (the “2012 EBI Plan”) and the FirstBank Preferred Equity Based Incentive Plan (the “Preferred EBI Plan” and, together with the 2010 EBI Plan and the 2012 EBI Plan, the “EBI Plans”). Prior to the initial public offering, awards granted under EBI Plans were settled in cash only. Following the initial public offering, participants in the EBI Plans were given the one-time option to elect, for each EBI Unit vested to such participant, either (i) an amount in cash or (ii) a number of shares of Company common stock determined pursuant to a conversion formula that took into account the effect of the initial public offering. Consistent with the terms of the EBI Plans and approved by the Board of Directors, outstanding EBI Units were adjusted to reflect the 100-for-one stock split that was effectuated prior to the IPO.

The Bank also has a separate deferred compensation agreement with one key executive.

Each plan or agreement is an unfunded general obligation of the Bank. The plans and agreements have varying vesting periods and other terms as follows:

2010 EBI Plan— Pursuant to the terms of the 2010 EBI Plan, each EBI Unit vests ratably over five years, or earlier upon a change of control, death or disability or retirement after age 65. On or shortly following the vesting date, the holder of an EBI Unit will receive an amount in cash (or, if so elected by the participant following the IPO, in stock) equal to the fair market value of a share of common stock on the December 31 immediately preceding the payment date. Prior to the IPO, fair market value was determined by dividing 7.5% of the total assets of the Bank by the total number of outstanding common stock shares of the Company. Following the IPO, EBI Units are valued based upon the Company’s stock price. Units under this plan became fully vested January, 2017.

Preferred EBI Plan—The Preferred EBI Plan has the same terms and conditions as those described above for the 2010 EBI Plan, with the exception of a seven year ratable vesting period. Units under this plan became fully vested January, 2017.

2012 EBI Plan— Pursuant to the terms of the 2012 EBI Plan, each EBI Unit vests and becomes payable following the third anniversary of the date of grant, or earlier upon a change of control, death or disability or retirement after age 65. On or shortly following the vesting date, the holder of an EBI Unit will receive an amount in cash (or, if so elected by the participant following the IPO, in stock) equal to the fair market value of a share of common stock on the December 31 immediately preceding the payment date. Following the IPO, EBI Units are valued based upon the Company’s stock price. Prior to the IPO, fair market value of the Company was determined based upon the average of the sum of (a) 15 times the Company’s after-tax earnings, based on a default tax rate imposed by the Code, and (b) 1.5 times the Company’s tangible book value, defined as the consolidated equity of the Company less unrealized gains (losses) and less goodwill and intangible assets. Following the IPO, EBI Units outstanding under the 2012 EBI Plan were adjusted to prevent dilution of these EBI Units as a result of the IPO pursuant to the following conversion formula: (i) the number of EBI Units outstanding under the 2012 EBI Plan (as adjusted for the stock split), multiplied by (ii) 1.13 (determined by dividing $21.4085, the fair market value per EBI Unit as determined under the 2012 EBI Plan, by $19.00, the IPO price).

Deferred compensation Agreement—Effective December 31, 2014, the Bank entered into an agreement with the Bank’s Chief Executive Officer to reward his prior service, pursuant to which he is entitled to receive a fixed lump sum cash payment equal to $3,000,000 on December 31, 2019 or the earlier occurrence of his separation of service or a change in control of the Company. On August 19, 2016, the Bank entered into an amendment to the deferred compensation agreement, pursuant to which the deferred account is now denominated in 157,895 deferred stock units, determined by dividing $3,000,000 by $19.00 (the IPO price). The deferred stock units are convertible on a 1-for-1 basis into shares of Company common stock on the original payment date described above.

Summary—At December 31, 2018 and 2017, the accompanying consolidated balance sheet include liabilities for cash-settled awards under the EBI Plans amounted to $993 and $2,346, respectively. As of December 31, 2018 and 2017, there were 29,172 and 67,470 units, respectively, in the equity based incentive plan for those employees who elected cash settlement of EBI units. Subsequent to December 31, 2018, these cash-settled awards were fully distributed. For the year ended December 31, 2018 and 2017, the Company incurred expenses related to these plans and agreements totaling $3,787 and $3,685, respectively, which is included in salaries, commissions and employee benefits in the accompanying statement of income. Additionally, payments under the plans totaled $1,818 and $5,163, respectively, for 2018 and 2017.