Condensed Financial Information of First Commonwealth Financial Corporation (Parent Company Only) - Statements of Operations (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Condensed Financial Statements, Captions [Line Items]
Interest and dividends	$ 206,358	$ 219,075	$ 231,545
Interest expense	(21,707)	(30,146)	(41,678)
Other income	10,632	13,610	12,803
Applicable income tax (provision) benefits	(15,281)	(14,658)	380
Net Income	41,482	41,954	15,274
Parent [Member]
Condensed Financial Statements, Captions [Line Items]
Interest and dividends	1	1	1
Dividends from subsidiaries	65,140	64,342	10,321
Interest expense	(3,128)	(5,711)	(5,605)
Other income	2,653	12,581	30,595
Operating expense	(8,820)	(19,061)	(44,057)
Income (loss) before taxes and equity in undistributed earnings of subsidiaries	55,846	52,152	(8,745)
Applicable income tax (provision) benefits	3,384	4,364	6,618
Income (loss) before equity in undistributed earnings of subsidiaries	59,230	56,516	(2,127)
Equity in undistributed (loss) earnings of subsidiaries	(17,748)	(14,562)	17,401
Net Income	$ 41,482	$ 41,954	$ 15,274