Subordinated Debentures - Subordinated Debentures Outstanding (Detail) (USD $) In Thousands, unless otherwise specified	0 Months Ended	12 Months Ended
	Apr. 02, 2013	Dec. 31, 2013	Dec. 31, 2012
Subordinated Borrowing [Line Items]
Subordinated Debentures outstanding, Amount		$ 72,167	$ 105,750
First Commonwealth Capital Trust I [Member]
Subordinated Borrowing [Line Items]
Subordinated Debentures outstanding, Due		Jan. 01, 2029
Subordinated Debentures outstanding, Amount		0	33,583
Fixed interest rate	9.50%		9.50%
First Commonwealth Capital Trust II [Member]
Subordinated Borrowing [Line Items]
Subordinated Debentures outstanding, Due		Jan. 01, 2034
Subordinated Debentures outstanding, Amount		30,929	30,929
First Commonwealth Capital Trust III [Member]
Subordinated Borrowing [Line Items]
Subordinated Debentures outstanding, Due		Jan. 01, 2034
Subordinated Debentures outstanding, Amount		$ 41,238	$ 41,238
Subordinated Debt [Member] | LIBOR [Member] | First Commonwealth Capital Trust II [Member]
Subordinated Borrowing [Line Items]
Variable interest rate		2.85%	2.85%
Subordinated Debt [Member] | LIBOR [Member] | First Commonwealth Capital Trust III [Member]
Subordinated Borrowing [Line Items]
Variable interest rate		2.85%	2.85%