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Subordinated Debentures - Additional Information (Detail) $ in Thousands | 12 Months Ended
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Dec. 31, 2017 USD ($) trust | Dec. 31, 2016
Subordinated Borrowing [Line Items] |  |
Number of trusts | trust | 2 |
First Commonwealth Capital Trust III [Member] |  |
Subordinated Borrowing [Line Items] |  |
Redemption price as percentage of principal amount | 100.00% |
Deferred finance costs | $ 630 |
First Commonwealth Capital Trust II [Member] |  |
Subordinated Borrowing [Line Items] |  |
Redemption price as percentage of principal amount | 100.00% |
Deferred finance costs | $ 471 |
LIBOR [Member] | Subordinated Debt [Member] | First Commonwealth Capital Trust III [Member] |  |
Subordinated Borrowing [Line Items] |  |
Variable interest rate | 2.85% | 2.85%
LIBOR [Member] | Subordinated Debt [Member] | First Commonwealth Capital Trust II [Member] |  |
Subordinated Borrowing [Line Items] |  |
Variable interest rate | 2.85% | 2.85%

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- Definition Number of Trusts + References No definition available. + Details
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- Definition Redemption Price As Percentage Of Principal Amount + References No definition available. + Details
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- Definition Percentage points added to the reference rate to compute the variable rate on the debt instrument. + References No definition available. + Details
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- Definition Amount, before accumulated amortization, of debt issuance costs. Includes, but is not limited to, legal, accounting, underwriting, printing, and registration costs. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 835 -SubTopic 30 -Section 45 -Paragraph 3 -URI http://asc.fasb.org/extlink&oid=64930785&loc=d3e28555-108399 + Details
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- Definition 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. + References No definition available. + Details
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- Details
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- Details
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- Details
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- Details
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