Business Combination - Capstone Merger (Details) - Capstone Bancshares Inc. [Member] $ / shares in Units, $ in Thousands	Nov. 01, 2017 USD ($) $ / shares shares
Business Acquisition [Line Items]
Estimated common stock issued (in shares) \| shares	2,908,094
Market price of SMBK common stock (in dollars per share) \| $ / shares	$ 23.49
Estimated fair value of SMBK common stock issued (in shares)	$ 68,311
Estimated fair value of Capstone stock options	1,585
Cash consideration paid	15,826
Total consideration	85,722
Fair value of assets acquired and liabilities assumed:
Cash and cash equivalents	16,810
Investment securities available for sale	51,638
Restricted investments	1,049
Loans	413,023
Premises and equipment	8,668
Bank owned life insurance	10,031
Core deposit intangible	5,530
Other real estate owned	410
Prepaid and other assets	6,360
Deposits	(454,154)
FHLB advances and other borrowings	(4,887)
Payables and other liabilities	(6,803)
Total fair value of net assets acquired	47,675
Goodwill	$ 38,047

The amount of assets acquired and liabilities assumed bank owned life insurance.

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The amount of Assets Acquired and Liabilities Assumed Core Deposit Intangible.

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The amount of assets acquired and liabilities assumed deposits liability.

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Business Combination, Recognized Identifiable Assets Acquired And Liabilities Assumed, Investment Owned Restricted Cost

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The amount of assets acquired and liabilities assumed other real estate owned.

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Number of shares of equity interests issued or issuable to acquire entity.

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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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Price of a single share of a number of saleable stocks paid or offered to be paid in a business combination.

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Amount of consideration transferred, consisting of acquisition-date fair value of assets transferred by the acquirer, liabilities incurred by the acquirer, and equity interest issued by the acquirer.

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Amount of equity interests of the acquirer, including instruments or interests issued or issuable in consideration for the business combination.

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Amount of tangible or intangible assets, including a business or subsidiary of the acquirer transferred by the entity to the former owners of the acquiree. Excludes cash.

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Amount of currency on hand as well as demand deposits with banks or financial institutions, acquired at the acquisition date. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates.

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Amount of investments in debt and equity securities, including, but not limited to, held-to-maturity, trading and available-for-sale expected to be converted to cash, sold or exchanged within one year or the normal operating cycle, if longer, acquired at the acquisition date.

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Amount of asset related to consideration paid in advance for costs that provide economic benefits in future periods, and amount of other assets that are expected to be realized or consumed within one year or the normal operating cycle, if longer, acquired at the acquisition date.

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Amount due from customers or clients for goods or services, including trade receivables, that have been delivered or sold in the normal course of business, and amounts due from others, including related parties expected to be converted to cash, sold or exchanged within one year or the normal operating cycle, if longer, acquired at the acquisition date.

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Amount of liabilities incurred for goods and services received that are used in an entity's business and related party payables, assumed at the acquisition date.

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Amount recognized as of the acquisition date for the identifiable assets acquired in excess of (less than) the aggregate liabilities assumed.

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Amount of long-term debt due after one year or the normal operating cycle, if longer, assumed at the acquisition date.

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The amount of property, plant, and equipment recognized as of the acquisition date.

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Amount after accumulated impairment loss of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

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The cash outflow associated with the acquisition of business during the period. The cash portion only of the acquisition price.

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