Condensed Financial Information of First Commonwealth Financial Corporation (parent company only) - Statements of Cash Flow (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Operating Activities
Net Income	$ 128,181	$ 138,257	$ 73,447
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	10,552	11,442	11,653
Other net	15,413	(5,874)	5,349
Net cash provided by operating activities	151,413	165,046	105,699
Investing Activities
Net cash used in investing activities	(588,788)	(565,305)	(483,138)
Financing Activities
Dividends paid	(44,578)	(43,611)	(42,982)
Proceeds from reissuance of treasury stock	245	222	222
Purchase of treasury stock	(15,598)	(31,301)	(20,905)
Net cash provided by financing activities	196,247	439,050	612,164
Net (decrease) increase in cash and cash equivalents	(241,128)	38,791	234,725
Parent Company [Member]
Operating Activities
Net Income	128,181	138,257	73,447
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	335	369	383
Net gains on sales of assets	(113)	228	0
Decrease (increase) in prepaid income taxes	0	317	(317)
Undistributed equity in subsidiaries	(42,276)	(72,330)	(17,996)
Other net	0	(14,830)	19,705
Net cash provided by operating activities	86,127	52,011	75,222
Investing Activities
Net change in loans	2	2	1
Payments to Acquire Property and Equipment	(152)	(101)	(20)
Net cash used in investing activities	(150)	(99)	(19)
Financing Activities
Dividends paid	(44,578)	(43,611)	(42,982)
Proceeds from reissuance of treasury stock	245	222	222
Purchase of treasury stock	(15,598)	(31,301)	(20,905)
Net cash provided by financing activities	(59,931)	(74,690)	(63,665)
Net (decrease) increase in cash and cash equivalents	26,046	(22,778)	11,538
Cash and cash equivalents at January 1	11,649	34,427	22,889
Cash and cash equivalents at December 31	$ 37,695	$ 11,649	$ 34,427