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Percentage of fourth anniversary of grant date.

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Percentage of incentive stock options vested on second anniversary of grant date.

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Percentage of incentive of third anniversary of grant date.

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Percentage of non qualified stock options vested on first anniversary of grant date.

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Percentage of non qualified stock options vested on second anniversaries of grant date.

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Share-based Compensation Arrangement, Ownership Percentage by Individual

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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.

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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.

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Amount of deferred tax expense from write-off of the deferred tax asset related to deductible stock options at exercise.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Amount of cost for defined contribution plan.

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Percentage of employees' gross pay for which the employer contributes a matching contribution to a defined contribution plan.

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Percentage employer matches of the employee's percentage contribution matched.

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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.

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- Definition

Unrecognized cost of unvested share-based awards, other than options, awarded to employees as compensation.

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- Definition

Unrecognized cost of unvested options awarded to employees as compensation.

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Amount of cash inflow from exercise of stock options granted under share-based compensation arrangement.

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Period which an employee's right to exercise an award is no longer contingent on satisfaction of either a service condition, market condition or a performance condition, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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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).

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The weighted average fair value at grant date for nonvested equity-based awards issued 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).

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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).

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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.

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- Definition

Gross number of share options (or share units) granted during the period.

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No definition available.

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The weighted average grant-date fair value of options granted during the reporting period as calculated by applying the disclosed option pricing methodology.

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Amount by which the current fair value of the underlying stock exceeds the exercise price of options outstanding.

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Number of options outstanding, including both vested and non-vested options.

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Period from grant date that an equity-based award expires, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Amount of difference between fair value of the underlying shares reserved for issuance and exercise price of vested portions of options outstanding and currently exercisable.

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Fair value of options vested. Excludes equity instruments other than options, for example, but not limited to, share units, stock appreciation rights, restricted stock.

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Purchase price of common stock expressed as a percentage of its fair value.

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The noncash expense that accounts for the value of stock or unit options distributed to employees as compensation.

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Employee Benefit Plans (FY) (Details Textual) - USD ($)		12 Months Ended
Employee Benefit Plans (FY) (Details Textual) - USD ($)	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
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%