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Employee Benefit Plans - Narrative (Details) - USD ($) | 3 Months Ended | 12 Months Ended
--- | --- | ---
Mar. 31, 2017 | Mar. 31, 2016 | Dec. 31, 2016
Defined Benefit Plan Disclosure [Line Items] |  |  |
Share-based compensation expense | $ 26,812 | $ 33,635 |
Options vested in period, fair value | 0 | 19,425 |
Deferred tax expense from stock options exercised | 0 | 0 |
Options, exercises in period, intrinsic value | 5,024,759 |  |
Options, outstanding, intrinsic value | 2,266,259 |  |
Options, exercisable, intrinsic value | 2,034,800 |  |
Proceeds from stock options exercised | $ 4,260,734 |  |
Number of shares granted | 0 |  | 0
Deferred Salary Reduction Plan [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined contribution plan, cost recognized | $ 102,716 | $ 90,856 |
Director [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Direct stock grant expense | 31,791 |  |
Stock Options [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Unrecognized compensation costs | $ 340,542 |  |
Unrecognized compensation costs, period for recognition | 1 year 4 months 24 days |  |
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% |  |
Smart Bank Stock Option Plan [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Number of shares authorized | 525,000 |  |
Exercise price, not less than (as a percent) | 100.00% |  |
Legacy Smart Financial Inc 2010 Incentive Plan [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Number of shares authorized | 525,000 |  |
Exercise price, not less than (as a percent) | 100.00% |  |
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% |  |
401 (k) Matching Range One [Member] | Deferred Salary Reduction Plan [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Employer matching contribution, percent of employees gross pay | 3.00% |  |
Employer matching contribution, percent of match | 100.00% |  |
401 (k) Matching Range Two [Member] | Deferred Salary Reduction Plan [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Employer matching contribution, percent of employees gross pay | 2.00% |  |
Employer matching contribution, percent of match | 50.00% |  |

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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=6415400&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=6415400&loc=d3e5070-113901 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Staff Accounting Bulletin (SAB) -Number Topic 14 -Section F + 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=32706628&loc=d3e11283-113907 + Details
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- Definition Weighted average period over which unrecognized compensation is expected to be recognized for equity-based compensation plans, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. + 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 (i) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 + Details
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- Definition The maximum number of shares (or other type of equity) originally approved (usually by shareholders and board of directors), net of any subsequent amendments and adjustments, for awards under the equity-based compensation plan. As stock or unit options and equity instruments other than options are awarded to participants, the shares or units remain authorized and become reserved for issuance under outstanding awards (not necessarily vested). + 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 (a)(3) -URI http://asc.fasb.org/extlink&oid=6415400&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=6415400&loc=d3e5070-113901 + Details
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- Definition Amount by which the current fair value of the underlying stock exceeds the exercise price of options outstanding. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 + Details
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- Definition Number of options outstanding, including both vested and non-vested options. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(1)(i)-(ii) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 + Details
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