Regulatory Restrictions and Capital Adequacy - Schedule of Capital Amount and Ratio Considered to be Capitalized (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Well Capitalized Regulatory Guidelines [Member] | First Commonwealth Bank [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Total Capital to Risk Weighted Assets, Well Capitalized Regulatory Guidelines	$ 495,344	$ 486,776
Tier I Capital to Risk Weighted Assets, Well Capitalized Regulatory Guidelines, Capital Amount	297,206	292,066
Tier I Capital to Average Assets, Well Capitalized Regulatory Guidelines, Capital Amount	297,491	285,680
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	6.00%	6.00%
Tier I Capital to Average Assets, Well Capitalized Regulatory Guidelines Ratio	5.00%	5.00%
Regulatory Minimum [Member] | First Commonwealth Bank [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Total Capital to Risk Weighted Assets, Regulatory Minimum Capital Amount	396,275	389,421
Tier I Capital to Risk Weighted Assets, Regulatory Minimum Capital Amount	198,138	194,710
Tier I Capital to Average Assets, Regulatory Minimum Capital Amount	237,993	228,544
Total Capital to Risk Weighted Assets, Regulatory Minimum Ratio	8.00%	8.00%
Tier I Capital to Risk Weighted Assets, Regulatory Minimum Ratio	4.00%	4.00%
Tier I Capital to Average Assets, Regulatory Minimum Ratio	4.00%	4.00%
Regulatory Minimum [Member] | First Commonwealth Financial Corporation [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Total Capital to Risk Weighted Assets, Regulatory Minimum Capital Amount	396,009	390,173
Tier I Capital to Risk Weighted Assets, Regulatory Minimum Capital Amount	198,004	195,087
Tier I Capital to Average Assets, Regulatory Minimum Capital Amount	239,430	230,322
Total Capital to Risk Weighted Assets, Regulatory Minimum Ratio	8.00%	8.00%
Tier I Capital to Risk Weighted Assets, Regulatory Minimum Ratio	4.00%	4.00%
Tier I Capital to Average Assets, Regulatory Minimum Ratio	4.00%	4.00%
Actual [Member] | First Commonwealth Bank [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Total Capital to Risk Weighted Assets	637,415	669,131
Tier I Capital to Risk Weighted Assets	580,031	608,176
Tier I Capital to Average Assets	580,031	608,176
Total Capital to Risk Weighted Assets, Ratio	12.87%	13.75%
Tier I Capital to Risk Weighted Assets, Ratio	11.71%	12.49%
Tier I Capital to Average Assets, Ratio	9.75%	10.64%
Actual [Member] | First Commonwealth Financial Corporation [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Total Capital to Risk Weighted Assets	656,235	708,583
Tier I Capital to Risk Weighted Assets	598,851	647,460
Tier I Capital to Average Assets	$ 598,851	$ 647,460
Total Capital to Risk Weighted Assets, Ratio	13.26%	14.53%
Tier I Capital to Risk Weighted Assets, Ratio	12.10%	13.28%
Tier I Capital to Average Assets, Ratio	10.00%	11.24%