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Employee Benefit Plans (Details Textual) - USD ($) |  | 12 Months Ended
--- | --- | ---
Aug. 04, 2017 | Dec. 31, 2017 | Dec. 31, 2016
Defined Benefit Plan Disclosure [Line Items] |  |  |
Deferred compensation arrangements, overall, description |  | After one year of service the Company matches 100 percent of employee contributions up to 3 percent of compensation and 50 percent of employee contributions on the next 2 percent of compensation. |
Share-based compensation expense |  | $ 97,966 | $ 132,635
Options vested in period, fair value |  | 313,977 | 95,658
Deferred tax expense from stock options exercised |  | 1,331,689 | 252,931
Options, exercises in period, intrinsic value |  | 5,468,780 | $ 660,476
Options, outstanding, intrinsic value |  | 3,261,940 |
Options, exercisable, intrinsic value |  | 3,105,964 |
Proceeds from stock options exercised |  | $ 4,885,646 |
Number of shares granted |  | 0 | 0
Weighted average grant-date fair value, granted (in dollars per share) |  | $ 0.00 |
Director [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Direct stock grant expense |  | $ 31,791 | $ 0
Deferred Salary Reduction Plan [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined contribution plan, cost recognized |  | 427,975 | 403,309
Stock Options [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Unrecognized compensation costs |  | $ 258,000 |
Unrecognized compensation costs, period for recognition |  | 11 months 16 days |
Stock Appreciation Rights (SARs) [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Share-based compensation expense |  | $ 21,829 | 0
Restricted Stock [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Number of shares granted |  | 27,500 |
Legacy Cornerstone Bancshares, Inc. Long-Term Incentive Plan [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Exercise price, not less than (as a percent) |  | 100.00% |
Legacy Smart Financial Inc 2010 Incentive Plan [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Exercise price, not less than (as a percent) |  | 100.00% |
Number of shares authorized |  | 525,000 |
Stock Incentive Plan Two Thousand Fifteen [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Exercise price, not less than (as a percent) |  | 110.00% |
Number Outstanding (in shares) |  | 2,000,000 |
Term of options, no more than |  | 10 years |
Voting power held by participant (as a percent) |  | 10.00% |
Term of option to participants with more than ten percent voting power |  | 5 years |
Percentage Of incentive stock options vesting on second anniversary |  | 30.00% |
Percentage Of incentive stock options vesting on third anniversary |  | 30.00% |
Percentage Of incentive stock options vesting on fourth anniversary |  | 40.00% |
Percentage Of nonqualified stock options vesting on first anniversary |  | 50.00% |
Percentage Of nonqualified stock options vesting on second anniversary |  | 50.00% |
Stock Incentive Plan Two Thousand Fifteen [Member] | Restricted Stock [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Term of option to participants with more than ten percent voting power |  | 5 years |
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value | $ 24.58 |  |
Share-based compensation expense |  | $ 56,330 | $ 0
Number of shares granted | 27,500 |  |
Employee Service Share-based Compensation, Nonvested Awards, Compensation Not yet Recognized, Share-based Awards Other than Options |  | $ 619,620 |
401 (k) Matching Range One [Member] | Deferred Salary Reduction Plan [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Request service period |  | 1 year |
Employer matching contribution, percent of match |  | 100.00% |
Employer matching contribution, percent of employees gross pay |  | 3.00% |
401 (k) Matching Range Two [Member] | Deferred Salary Reduction Plan [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Employer matching contribution, percent of match |  | 50.00% |
Employer matching contribution, percent of employees gross pay |  | 2.00% |

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- Definition Represents the expense recognized during the period arising from equity-based compensation arrangements (for example, shares of stock, unit, stock options or other equity instruments) with employees, directors and certain consultants qualifying for treatment as employees. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SAB Topic 14.F) -URI http://asc.fasb.org/extlink&oid=27013229&loc=d3e301413-122809 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 1 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5047-113901 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (h)(1)(i) -URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901 + Details
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- Definition General description of deferred compensation arrangements. Deferred compensation represents currently earned compensation that, under the terms of a profit-sharing, rabbi trust, pension, employee contract, or equity-based (including stock or unit option) plan, is not actually paid until a later date and is therefore not taxable until that date. May also include some split-dollar life insurance arrangements. This type of arrangement is usually made to help employees postpone paying taxes on the income and also to retain employees longer. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5047-113901 + Details
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- Definition Amount of deferred tax expense from write-off of the deferred tax asset related to deductible stock options at exercise. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 20 -Section 55 -Paragraph 20 -URI http://asc.fasb.org/extlink&oid=96864182&loc=d3e11283-113907 + Details
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- Definition The number of grants made during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan). + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(2)(iii)(1) -URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901 + Details
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- Definition Amount of accumulated difference between fair value of underlying shares on dates of exercise and exercise price on options exercised (or share units converted) into shares. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (d)(2) -URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901 + Details
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