Fair Values of Assets and Liabilities - Carrying Amounts and Fair Values of Financial Instruments (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011	Sep. 30, 2011
Fair Value Measurements Of Financial Instruments [Line Items]
Cash and due from banks	$ 85,183	$ 74,967
Interest-bearing deposits	3,881	3,511
Securities available for sale	1,130,822	1,142,776
Other investments	32,479	39,796
Loans held for sale	0	13,412
Loans	4,214,299	4,043,643	3,973,723
Deposits	4,494,434	4,504,684
Short-term borrowings	461,770	312,777
Long-term debt	74,721	101,664
Subordinated debt	105,750	105,750
Level 1 [Member]
Fair Value Measurements Of Financial Instruments [Line Items]
Other investments	0	0
Level 2 [Member]
Fair Value Measurements Of Financial Instruments [Line Items]
Other investments	32,479	39,796
Level 3 [Member]
Fair Value Measurements Of Financial Instruments [Line Items]
Other investments	0	0
Carrying Amount [Member]
Fair Value Measurements Of Financial Instruments [Line Items]
Cash and due from banks	85,183	74,967
Interest-bearing deposits	3,881	3,511
Securities available for sale	1,130,822	1,142,776
Other investments	32,479	39,796
Loans held for sale		13,412
Loans	4,214,299	4,043,643
Deposits	4,494,434	4,504,684
Short-term borrowings	461,770	312,777
Long-term debt	74,721	101,664
Subordinated debt	105,750	105,750
Estimated Fair Value [Member]
Fair Value Measurements Of Financial Instruments [Line Items]
Cash and due from banks	85,183	74,967
Interest-bearing deposits	3,881	3,511
Securities available for sale	1,130,822	1,142,776
Other investments	32,479	39,796
Loans held for sale		13,412
Loans	4,269,822	4,113,525
Deposits	4,435,555	4,452,235
Short-term borrowings	461,760	312,777
Long-term debt	77,470	103,749
Subordinated debt	76,995	75,310
Estimated Fair Value [Member] \| Level 1 [Member]
Fair Value Measurements Of Financial Instruments [Line Items]
Cash and due from banks	85,183
Interest-bearing deposits	3,881
Securities available for sale	440
Other investments	0
Loans	0
Deposits	0
Short-term borrowings	0
Long-term debt	0
Subordinated debt	0
Estimated Fair Value [Member] \| Level 2 [Member]
Fair Value Measurements Of Financial Instruments [Line Items]
Cash and due from banks	0
Interest-bearing deposits	0
Securities available for sale	1,105,911
Other investments	32,479
Loans	59,241
Deposits	4,435,555
Short-term borrowings	461,760
Long-term debt	77,470
Subordinated debt	0
Estimated Fair Value [Member] \| Level 3 [Member]
Fair Value Measurements Of Financial Instruments [Line Items]
Cash and due from banks	0
Interest-bearing deposits	0
Securities available for sale	24,471
Other investments	0
Loans	4,210,581
Deposits	0
Short-term borrowings	0
Long-term debt	0
Subordinated debt	$ 76,995

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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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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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