Subordinated Debentures - Additional Information (Detail) $ in Thousands	12 Months Ended
	Dec. 31, 2016 USD ($) trust	Dec. 31, 2015
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%