Loans and Allowance for Credit Losses - Additional Information (Detail) (USD $)	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013	Dec. 31, 2013
Accounts, Notes, Loans and Financing Receivable [Line Items]
Increase (decrease) in nonperforming loans	$ (3,200,000)
Charge-offs	3,646,000	10,476,000
Decrease in specific allowance for nonperforming loans	(1,700,000)
Unfunded commitments related to nonperforming loans	3,400,000
Off balance sheet reserve to nonperforming loans	100,000
Loans held for sale	0
Total gains or losses included in earnings	0	126,000
Nonaccrual	45,680,000		45,888,000
Recorded investment	56,203,000		59,383,000
Troubled debt restructured loans decreased	7,600,000
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	300,000
Loans with modifications to rate and payment due to reamortization	200,000	475,000
Loans Held For Sale [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total gains or losses included in earnings	0	126,000
Gas Drilling Related Business in Louisiana [Member] | Nonaccrual Commercial Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Recorded investment	8,000,000
Western Pennsylvania Specialty Metal Processor [Member] | Nonaccrual Commercial Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Nonaccrual	3,200,000
Non Accrual Loans [Member] | Local Energy Company [Member] [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Nonaccrual	10,900,000
Non Accrual Loans [Member] | Western Pennsylvania Real Estate Developer [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Nonaccrual	2,400,000
Impaired Loan Receivable, Original Balance	44,100,000
Total charge-offs recognized	28,500,000
Loans Sold [Domain]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Increase (decrease) in nonperforming loans	700,000
Nonaccrual Loans Paid Off [Domain]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Increase (decrease) in nonperforming loans	6,900,000
Additions to Nonperforming Loans [Domain]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Increase (decrease) in nonperforming loans	9,600,000
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
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
Nonaccrual Loans Paid Off [Domain]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Decrease In Troubled Debt Restructurings	6,600,000
Western Pennsylvania Reals Estate Investor [Member] | Nonaccrual Loans Paid Off [Domain]
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 [Domain]
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 [Domain]
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 [Domain]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Increase (decrease) in nonperforming loans	600,000
Nonaccrual Commercial Loans [Member] | Additions to Nonperforming Loans [Domain]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Increase (decrease) in nonperforming loans	8,000,000
Nonaccrual Consumer Loans [Member] | Additions to Nonperforming Loans [Domain]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Increase (decrease) in nonperforming loans	1,100,000
Local Energy Company [Member] [Member] | Charge-offs [Domain]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Charge-offs	500,000
Western Pennsylvania [Member] | Charge-offs [Domain]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Charge-offs	600,000
Consumer Home Equity Loan [Member] | Charge-offs [Domain]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Charge-offs	$ 400,000