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Commitments and Contingencies - Allowance for Credit Losses on Unfunded Commitments (Details) - USD ($) $ in Thousands | 3 Months Ended
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Mar. 31, 2022 | Mar. 31, 2021
Commitments and Contingencies [Roll Forward] |  |
Balance at beginning of period | $ 125,559 | $ 170,389
Balance at end of period | 120,049 | 157,954
Unfunded Commitments |  |
Commitments and Contingencies [Roll Forward] |  |
Balance at beginning of period | 14,380 | 16,378
Provision for credit losses on unfunded commitments | 1,882 | (2,222)
Balance at end of period | $ 16,262 | $ 14,156

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- Definition Commitments and Contingencies [Roll Forward] + References No definition available. + Details
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- Definition Provision For Credit Losses + References No definition available. + Details
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Namespace Prefix: | fbk_
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Balance Type: | debit
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- Definition Amount excluding accrued interest, of allowance for credit loss on financing receivable. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 20 -Section 45 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=124255206&loc=SL82895884-210446 + Details
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Balance Type: | credit
Period Type: | instant

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- Details
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