Condensed Financial Information of First Commonwealth Financial Corporation (Parent Company Only) - Statements of Financial Condition (Detail) - USD ($) $ in Thousands	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Assets
Loans	$ 7,539,237	$ 6,746,708
Premises and equipment, net	115,106	120,775
Other assets	199,255	128,268
Total assets	9,805,666	9,545,093
Liabilities and Shareholders' Equity
Subordinated Debentures outstanding, Amount	170,937	170,775
Shareholders' equity	1,052,074	1,109,372	$ 1,068,617	$ 1,055,665
Total liabilities and shareholders’ equity	9,805,666	9,545,093
Parent Company [Member]
Assets
Cash	37,695	11,649
Loans	8	9
Investment in subsidiaries	1,061,285	1,152,580
Investment in unconsolidated subsidiary trusts	2,200	2,181
Investment in Jointly-Owned Company	394	357
Premises and equipment, net	3,098	3,244
Dividends receivable from subsidiaries	5,428	7,762
Other assets	21,345	8,212
Total assets	1,131,453	1,185,994
Liabilities and Shareholders' Equity
Accrued expenses and other liabilities	7,212	4,455
Subordinated Debentures outstanding, Amount	72,167	72,167
Shareholders' equity	1,052,074	1,109,372
Total liabilities and shareholders’ equity	$ 1,131,453	$ 1,185,994