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Regulatory Restrictions and Capital Adequacy - Schedule of Capital Amount and Ratio Considered to be Capitalized (Detail) - USD ($) $ in Thousands | Dec. 31, 2015 | Dec. 31, 2014
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First Commonwealth Financial Corporation |  |
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items] |  |
Tier 1 Common Equity to Risk Weighted Assets | $ 556,939 |
Tier 1 Common Equity to Risk Weighted Assets | 10.00% |
Tier 1 Common Equity Required to be Well Capitalized | $ 362,091 |
Tier 1 Common Equity Required to be Well Capitalized to Risk Weighted Assets | 6.50% |
First Commonwealth Bank |  |
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items] |  |
Tier 1 Common Equity to Risk Weighted Assets | $ 535,814 |
Tier 1 Common Equity to Risk Weighted Assets | 9.62% |
Tier 1 Common Equity Required to be Well Capitalized | $ 362,084 |
Tier 1 Common Equity Required to be Well Capitalized to Risk Weighted Assets | 6.50% |
Actual | First Commonwealth Financial Corporation |  |
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items] |  |
Total Capital to Risk Weighted Assets | $ 682,199 | $ 662,733
Tier I Capital to Risk Weighted Assets | 626,939 | 607,602
Tier I Capital to Average Assets | $ 626,939 | $ 607,602
Total Capital to Risk Weighted Assets, Ratio | 12.25% | 12.79%
Tier I Capital to Risk Weighted Assets, Ratio | 11.25% | 11.73%
Tier I Capital to Average Assets, Ratio | 9.85% | 9.85%
Actual | First Commonwealth Bank |  |
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items] |  |
Total Capital to Risk Weighted Assets | $ 656,244 | $ 647,500
Tier I Capital to Risk Weighted Assets | 600,984 | 592,369
Tier I Capital to Average Assets | $ 600,984 | $ 592,369
Total Capital to Risk Weighted Assets, Ratio | 11.78% | 12.48%
Tier I Capital to Risk Weighted Assets, Ratio | 10.79% | 11.41%
Tier I Capital to Average Assets, Ratio | 9.46% | 9.66%
Minimum Capital Required - Basel III Phase-In Schedule | First Commonwealth Financial Corporation |  |
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items] |  |
Total Capital to Risk Weighted Assets, Regulatory Minimum Capital Amount | $ 445,650 |
Tier I Capital to Risk Weighted Assets, Regulatory Minimum Capital Amount | 334,237 |
Tier I Capital to Average Assets, Regulatory Minimum Capital Amount | 254,631 |
Tier 1 Common Equity Required for Capital Adequacy | $ 250,678 |
Total Capital to Risk Weighted Assets, Regulatory Minimum Ratio | 8.00% |
Tier I Capital to Risk Weighted Assets, Regulatory Minimum Ratio | 6.00% |
Tier I Capital to Average Assets, Regulatory Minimum Ratio | 4.00% |
Tier 1 Common Equity Required for Capital Adequacy to Risk Weighted Assets | 4.50% |
Minimum Capital Required - Basel III Phase-In Schedule | First Commonwealth Bank |  |
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items] |  |
Total Capital to Risk Weighted Assets, Regulatory Minimum Capital Amount | $ 445,642 |
Tier I Capital to Risk Weighted Assets, Regulatory Minimum Capital Amount | 334,231 |
Tier I Capital to Average Assets, Regulatory Minimum Capital Amount | 254,095 |
Tier 1 Common Equity Required for Capital Adequacy | $ 250,673 |
Total Capital to Risk Weighted Assets, Regulatory Minimum Ratio | 8.00% |
Tier I Capital to Risk Weighted Assets, Regulatory Minimum Ratio | 6.00% |
Tier I Capital to Average Assets, Regulatory Minimum Ratio | 4.00% |
Tier 1 Common Equity Required for Capital Adequacy to Risk Weighted Assets | 4.50% |
Minimum Capital Required - Basel III Fully Phased-In | First Commonwealth Financial Corporation |  |
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items] |  |
Total Capital to Risk Weighted Assets, Regulatory Minimum Capital Amount | $ 584,915 |
Tier I Capital to Risk Weighted Assets, Regulatory Minimum Capital Amount | 473,503 |
Tier I Capital to Average Assets, Regulatory Minimum Capital Amount | 254,631 |
Tier 1 Common Equity Required for Capital Adequacy | $ 389,944 |
Total Capital to Risk Weighted Assets, Regulatory Minimum Ratio | 10.50% |
Tier I Capital to Risk Weighted Assets, Regulatory Minimum Ratio | 8.50% |
Tier I Capital to Average Assets, Regulatory Minimum Ratio | 4.00% |
Tier 1 Common Equity Required for Capital Adequacy to Risk Weighted Assets | 7.00% |
Minimum Capital Required - Basel III Fully Phased-In | First Commonwealth Bank |  |
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items] |  |
Total Capital to Risk Weighted Assets, Regulatory Minimum Capital Amount | $ 584,905 |
Tier I Capital to Risk Weighted Assets, Regulatory Minimum Capital Amount | 473,494 |
Tier I Capital to Average Assets, Regulatory Minimum Capital Amount | 254,095 |
Tier 1 Common Equity Required for Capital Adequacy | $ 389,937 |
Total Capital to Risk Weighted Assets, Regulatory Minimum Ratio | 10.50% |
Tier I Capital to Risk Weighted Assets, Regulatory Minimum Ratio | 8.50% |
Tier I Capital to Average Assets, Regulatory Minimum Ratio | 4.00% |
Tier 1 Common Equity Required for Capital Adequacy to Risk Weighted Assets | 7.00% |
Regulatory Minimum | First Commonwealth Financial Corporation |  |
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items] |  |
Total Capital to Risk Weighted Assets, Regulatory Minimum Capital Amount |  | $ 414,460
Tier I Capital to Risk Weighted Assets, Regulatory Minimum Capital Amount |  | 207,230
Tier I Capital to Average Assets, Regulatory Minimum Capital Amount |  | $ 246,738
Total Capital to Risk Weighted Assets, Regulatory Minimum Ratio |  | 8.00%
Tier I Capital to Risk Weighted Assets, Regulatory Minimum Ratio |  | 4.00%
Tier I Capital to Average Assets, Regulatory Minimum Ratio |  | 4.00%
Regulatory Minimum | First Commonwealth Bank |  |
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items] |  |
Total Capital to Risk Weighted Assets, Regulatory Minimum Capital Amount |  | $ 415,217
Tier I Capital to Risk Weighted Assets, Regulatory Minimum Capital Amount |  | 207,608
Tier I Capital to Average Assets, Regulatory Minimum Capital Amount |  | $ 245,276
Total Capital to Risk Weighted Assets, Regulatory Minimum Ratio |  | 8.00%
Tier I Capital to Risk Weighted Assets, Regulatory Minimum Ratio |  | 4.00%
Tier I Capital to Average Assets, Regulatory Minimum Ratio |  | 4.00%
Required to be Considered Well Capitalized | First Commonwealth Financial Corporation |  |
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items] |  |
Total Capital to Risk Weighted Assets, Well Capitalized Regulatory Guidelines | $ 557,062 |
Tier I Capital to Risk Weighted Assets, Well Capitalized Regulatory Guidelines, Capital Amount | 445,650 |
Tier I Capital to Average Assets, Well Capitalized Regulatory Guidelines, Capital Amount | $ 318,289 |
Total Capital to Risk Weighted Assets, Well Capitalized Regulatory Guidelines | 10.00% |
Tier I Capital to Risk Weighted Assets, Well Capitalized Regulatory Guidelines Ratio | 8.00% |
Tier I Capital to Average Assets, Well Capitalized Regulatory Guidelines Ratio | 5.00% |
Required to be Considered Well Capitalized | First Commonwealth Bank |  |
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items] |  |
Total Capital to Risk Weighted Assets, Well Capitalized Regulatory Guidelines | $ 557,052 | $ 519,021
Tier I Capital to Risk Weighted Assets, Well Capitalized Regulatory Guidelines, Capital Amount | 445,642 | 311,413
Tier I Capital to Average Assets, Well Capitalized Regulatory Guidelines, Capital Amount | $ 317,618 | $ 306,595
Total Capital to Risk Weighted Assets, Well Capitalized Regulatory Guidelines | 10.00% | 10.00%
Tier I Capital to Risk Weighted Assets, Well Capitalized Regulatory Guidelines Ratio | 8.00% | 6.00%
Tier I Capital to Average Assets, Well Capitalized Regulatory Guidelines Ratio | 5.00% | 5.00%

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