Loans and Allowance for Credit Losses - Additional Information (Detail) (USD $)	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013	Dec. 31, 2013
Accounts, Notes, Loans and Financing Receivable [Line Items]
Increase (decrease) in nonperforming loans			$ (14,100,000)
Allowance for Loan and Lease Losses Write-offs, Net			(12,100,000)
Charge-offs	2,880,000	5,583,000	14,629,000	32,195,000
Decrease in specific allowance for nonperforming loans			4,200,000
Unfunded commitments related to nonperforming loans	400,000		400,000
Off balance sheet reserve to nonperforming loans	0		0
Loans held for sale	1,305,000		1,305,000		0
Total gains or losses included in earnings	0	242,000	77,000	625,000
Nonaccrual	34,093,000		34,093,000		45,888,000
Recorded investment	45,257,000		45,257,000		59,383,000
Troubled debt restructured loans decreased			12,500,000
Loans to individuals [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non Accrual Status Of Loans After Number Of Days Past Due			150 days
Impaired Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commitments related to troubled debt restructured loans increased			500,000
Loans with modifications to rate and payment due to reamortization	100,000	100,000	500,000	588,000
Loans Held For Sale [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total gains or losses included in earnings	0	242,000	77,000	625,000
Audio Visual Equipment Distributer [Member] | Nonaccrual Commercial Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Recorded investment	3,900,000		3,900,000
Western Pennsylvania Specialty Metal Processor [Member] | Nonaccrual Commercial Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Nonaccrual	3,000,000		3,000,000
Non Accrual Loans [Member] | Local Energy Company [Member] [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Nonaccrual	10,600,000		10,600,000
Nonaccrual Loans Paid Off [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Increase (decrease) in nonperforming loans			12,500,000
Loans Sold [Domain]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Increase (decrease) in nonperforming loans			3,000,000
Additions to Nonperforming Loans [Domain]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Increase (decrease) in nonperforming loans			19,800,000
2012 Troubled Debt Restructuring [Member] | Non Accrual Loans [Member] | Local Energy Company [Member] [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Nonaccrual	2,700,000		2,700,000
2013 Troubled Debt Restructuring [Member] | Non Accrual Loans [Member] | Local Energy Company [Member] [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Nonaccrual	300,000		300,000
Nonaccrual Loans Paid Off [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Decrease In Troubled Debt Restructurings			11,300,000
Western Pennsylvania Funeral Home [Member] | Additions to Nonperforming Loans [Domain]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Increase (decrease) in nonperforming loans			700,000
Western Pennsylvania Personal Care Facility [Member] | Additions to Nonperforming Loans [Domain]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Increase (decrease) in nonperforming loans			700,000
Audio Visual Equipment Distributer [Member] | Additions to Nonperforming Loans [Domain]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Increase (decrease) in nonperforming loans			4,300,000
Residential Real Estate [Member] | Nonaccrual Loans Paid Off [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Increase (decrease) in nonperforming loans			900,000
Western Pennsylvania Real Estate Developer [Member] | Nonaccrual Loans Paid Off [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Increase (decrease) in nonperforming loans			4,700,000
Western Pennsylvania Reals Estate Investor [Member] | Nonaccrual Loans Paid Off [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Increase (decrease) in nonperforming loans			300,000
Western Pennsylvania Non-Profit Organization [Member] | Nonaccrual Loans Paid Off [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Increase (decrease) in nonperforming loans			3,100,000
Western Pennsylvania Reals Estate Manager [Member] | Nonaccrual Loans Paid Off [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Increase (decrease) in nonperforming loans			2,900,000
Western Pennsylvania Glass Manufacturer [Member] [Member] | Nonaccrual Loans Paid Off [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Increase (decrease) in nonperforming loans			600,000
Nonaccrual Consumer Loans [Member] | Additions to Nonperforming Loans [Domain]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Increase (decrease) in nonperforming loans			3,200,000
Gas Drilling Related Business in Louisiana [Member] | Charge Offs [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Charge-offs			5,800,000
Western Pennsylvania [Member] | Charge Offs [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Charge-offs			600,000
Local Energy Company [Member] [Member] | Charge Offs [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Charge-offs			$ 500,000