Subordinated Debentures Schedule of Subordinated Debentures Outstanding (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Debt Instrument [Line Items]
Subordinated debentures	$ 170,328	$ 170,288
First Commonwealth Bank 2028 [Member]
Debt Instrument [Line Items]
Subordinated debentures	49,152	49,131
First Commonwealth Bank 2033 [Member]
Debt Instrument [Line Items]
Subordinated debentures	49,009	48,990
First Commonwealth Capital Trust II [Member]
Debt Instrument [Line Items]
Subordinated debentures	30,929	30,929
First Commonwealth Capital Trust III [Member]
Debt Instrument [Line Items]
Subordinated debentures	$ 41,238	$ 41,238