Condensed Financial Information of First Commonwealth Financial Corporation (Parent Company Only) - Statements of Financial Condition (Detail) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Assets
Loans	$ 6,746,708	$ 6,659,874
Premises and equipment, net	120,775	125,517
Other assets	128,268	143,415
Total assets	9,545,093	9,068,104
Liabilities and Shareholders' Equity
Subordinated Debentures outstanding, Amount	170,775	170,612
Shareholders' equity	1,109,372	1,068,617	$ 1,055,665	$ 975,389
Total liabilities and shareholders’ equity	9,545,093	9,068,104
Parent Company [Member]
Assets
Cash	11,649	34,427
Loans	9	11
Investment in subsidiaries	1,152,580	1,108,801
Investment in unconsolidated subsidiary trusts	2,181	2,182
Investment in Jointly-Owned Company	357	338
Premises and equipment, net	3,244	3,476
Dividends receivable from subsidiaries	7,762	3,038
Other assets	8,212	7,307
Total assets	1,185,994	1,159,580
Liabilities and Shareholders' Equity
Accrued expenses and other liabilities	4,455	18,796
Subordinated Debentures outstanding, Amount	72,167	72,167
Shareholders' equity	1,109,372	1,068,617
Total liabilities and shareholders’ equity	$ 1,185,994	$ 1,159,580