Fair Values of Assets and Liabilities - Carrying Amounts and Fair Values of Financial Instruments (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014	Mar. 31, 2014
Fair Value Measurements Of Financial Instruments [Line Items]
Cash and due from banks	$ 62,161us-gaap_CashAndDueFromBanks	$ 72,276us-gaap_CashAndDueFromBanks
Interest-bearing deposits	3,124us-gaap_InterestBearingDepositsInBanks	2,262us-gaap_InterestBearingDepositsInBanks
Securities available for sale, at fair value	1,269,285us-gaap_AvailableForSaleSecurities	1,309,819us-gaap_AvailableForSaleSecurities
Held-to-maturity Securities	30,253us-gaap_HeldToMaturitySecurities
Other investments	47,076us-gaap_FederalHomeLoanBankStock	44,545us-gaap_FederalHomeLoanBankStock
Loans and Leases Receivable, Net of Deferred Income	4,437,601	4,457,308	4,252,213
Deposits	4,293,749us-gaap_Deposits	4,315,511us-gaap_Deposits
Short-term borrowings	1,125,520us-gaap_ShortTermBorrowings	1,105,876us-gaap_ShortTermBorrowings
Long-term debt	64,324us-gaap_OtherLongTermDebt	89,459us-gaap_OtherLongTermDebt
Subordinated debt	72,167us-gaap_SubordinatedDebt	72,167us-gaap_SubordinatedDebt
Level 1 [Member]
Fair Value Measurements Of Financial Instruments [Line Items]
Securities available for sale, at fair value	0	0
Other investments	0	0
Level 2 [Member]
Fair Value Measurements Of Financial Instruments [Line Items]
Securities available for sale, at fair value	1,236,231	1,279,400
Other investments	47,076	44,545
Level 3 [Member]
Fair Value Measurements Of Financial Instruments [Line Items]
Securities available for sale, at fair value	33,054	30,419
Other investments	0	0
Carrying Amount [Member]
Fair Value Measurements Of Financial Instruments [Line Items]
Cash and due from banks	62,161	72,276
Interest-bearing deposits	3,124	2,262
Securities available for sale, at fair value	1,269,285	1,309,819
Held-to-maturity Securities	30,253
Other investments	47,076	44,545
Loans Held for sale, Amount	5,892	2,502
Loans and Leases Receivable, Net of Deferred Income	4,437,601	4,457,308
Deposits	4,293,749	4,315,511
Short-term borrowings	1,125,520	1,105,876
Long-term debt	64,324	89,459
Subordinated debt	72,167	72,167
Estimate of Fair Value, Fair Value Disclosure [Member]
Fair Value Measurements Of Financial Instruments [Line Items]
Cash and due from banks	62,161	72,276
Interest-bearing deposits	3,124	2,262
Securities available for sale, at fair value	1,269,285	1,309,819
Held-to-maturity Securities	30,174
Other investments	47,076	44,545
Loans Held for sale, Amount	5,892	2,502
Loans and Leases Receivable, Net of Deferred Income	4,465,459	4,439,766
Deposits	4,297,771	4,319,997
Short-term borrowings	1,125,524	1,105,867
Long-term debt	65,255	90,319
Subordinated debt	63,069	62,815
Estimate of Fair Value, Fair Value Disclosure [Member] \| Level 1 [Member]
Fair Value Measurements Of Financial Instruments [Line Items]
Cash and due from banks	62,161	72,276
Interest-bearing deposits	3,124	2,262
Securities available for sale, at fair value	0	0
Held-to-maturity Securities	0
Other investments	0	0
Loans Held for sale, Amount	0	0
Loans and Leases Receivable, Net of Deferred Income	0	0
Deposits	0	0
Short-term borrowings	0	0
Long-term debt	0	0
Subordinated debt	0	0
Estimate of Fair Value, Fair Value Disclosure [Member] \| Level 2 [Member]
Fair Value Measurements Of Financial Instruments [Line Items]
Cash and due from banks	0	0
Interest-bearing deposits	0	0
Securities available for sale, at fair value	1,236,231	1,279,400
Held-to-maturity Securities	30,174
Other investments	47,076	44,545
Loans Held for sale, Amount	5,892	2,502
Loans and Leases Receivable, Net of Deferred Income	32,270	34,864
Deposits	4,297,771	4,319,997
Short-term borrowings	1,125,524	1,105,867
Long-term debt	65,255	90,319
Subordinated debt	0	0
Estimate of Fair Value, Fair Value Disclosure [Member] \| Level 3 [Member]
Fair Value Measurements Of Financial Instruments [Line Items]
Cash and due from banks	0	0
Interest-bearing deposits	0	0
Securities available for sale, at fair value	33,054	30,419
Held-to-maturity Securities	0
Other investments	0	0
Loans Held for sale, Amount	0	0
Loans and Leases Receivable, Net of Deferred Income	4,433,189	4,404,902
Deposits	0	0
Short-term borrowings	0	0
Long-term debt	0	0
Subordinated debt	$ 63,069	$ 62,815

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Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

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For banks and other depository institutions: Includes cash on hand (currency and coin), cash items in process of collection, noninterest bearing deposits due from other financial institutions (including corporate credit unions), and noninterest bearing balances with the Federal Reserve Banks, Federal Home Loan Banks and central banks.

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The aggregate of all deposit liabilities held by the entity, including foreign and domestic, interest and noninterest bearing; may include demand deposits, saving deposits, Negotiable Order of Withdrawal (NOW) and time deposits among others.

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Federal Home Loan Bank (FHLB) stock represents an equity interest in a FHLB. It does not have a readily determinable fair value because its ownership is restricted and it lacks a market (liquidity).

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Amount after other than temporary impairment (OTTI) accretion, of investments in debt securities classified as held-to-maturity.

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For banks and other depository institutions (including Federal Reserve Banks, if applicable): Interest-bearing deposits in other financial institutions for relatively short periods of time including, for example, certificates of deposits, which are presented separately from cash on the balance sheet.

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Amount before allowance and after deduction of deferred interest and fees, unamortized costs and premiums and discounts from face amounts, of loans and leases held in portfolio, including but not limited to, commercial and consumer loans. Excludes loans and leases covered under loss sharing agreements.

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The face amount of loans that will be sold to other entities.

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Including both current and noncurrent portions, carrying amount as of the balance sheet date of other forms of debt not elsewhere specified in the taxonomy with initial maturities beyond one year or beyond the normal operating cycle, if longer.

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Reflects the total carrying amount as of the balance sheet date of debt having initial terms less than one year or the normal operating cycle, if longer.

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Including the current and noncurrent portions, carrying value as of the balance sheet date of subordinated debt (with initial maturities beyond one year or beyond the operating cycle if longer). Subordinated debt places a lender in a lien position behind debt having a higher priority of repayment in liquidation of the entity's assets.

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