Condensed Financial Information of First Commonwealth Financial Corporation (Parent Company Only) - Statements of Financial Condition (Detail) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Assets
Loans	$ 4,829,162	$ 4,632,938
Premises and equipment, net	67,534	63,454
Other assets	84,648	103,717
Total assets	6,684,018	6,566,890
Liabilities and Shareholders' Equity
Subordinated debentures payable	72,167	72,167
Shareholders' equity	749,929	719,546	$ 716,145	$ 711,697
Total liabilities and shareholders’ equity	6,684,018	6,566,890
Parent [Member]
Assets
Cash	30,387	10,003
Loans	19	22
Investment in subsidiaries	770,214	719,073
Investment in unconsolidated subsidiary trusts	2,185	2,182
Investment in Jointly-Owned Company	9,042	8,978
Premises and equipment, net	3,793	3,780
Recievable from subsidiaries	33	441
Dividends receivable from subsidiaries	4,662	714
Other assets	2,453	47,631
Total assets	822,788	792,824
Liabilities and Shareholders' Equity
Accrued expenses and other liabilities	692	1,111
Subordinated debentures payable	72,167	72,167
Shareholders' equity	749,929	719,546
Total liabilities and shareholders’ equity	$ 822,788	$ 792,824