| **Fair Values of Assets and Liabilities - Carrying Amounts and Fair Values of Financial Instruments (Detail) (USD $)In Thousands, unless otherwise specified** | Jun. 30, 2014 | Dec. 31, 2013 | Jun. 30, 2013 |
|----------------------------------------------------------------------------------------------------------------------------------------------------------------|---------------|---------------|---------------|
| **Fair Value Measurements Of Financial Instruments [Line Items]**                                                                                              |          |          |          |
| Cash and due from banks                                                                                                                                        | $ 92,860      | $ 74,427      |          |
| Interest-bearing deposits                                                                                                                                      | 5,151         | 3,012         |          |
| Securities available for sale, at fair value                                                                                                                   | 1,347,611     | 1,318,365     |          |
| Other investments                                                                                                                                              | 44,077        | 35,444        |          |
| Loans                                                                                                                                                          | 4,334,214     | 4,283,833     | 4,229,752     |
| Deposits                                                                                                                                                       | 4,460,421     | 4,603,863     |          |
| Short-term borrowings                                                                                                                                          | 845,873       | 626,615       |          |
| Long-term debt                                                                                                                                                 | 136,672       | 144,385       |          |
| Subordinated debt                                                                                                                                              | 72,167        | 72,167        |          |
| 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                                                                                                                   | 1,318,037     | 1,293,422     |          |
| Other investments                                                                                                                                              | 44,077        | 35,444        |          |
| Level 3 [Member]                                                                                                                                               |          |          |          |
| **Fair Value Measurements Of Financial Instruments [Line Items]**                                                                                              |          |          |          |
| Securities available for sale, at fair value                                                                                                                   | 29,574        | 24,943        |          |
| Other investments                                                                                                                                              | 0             | 0             |          |
| Carrying Amount [Member]                                                                                                                                       |          |          |          |
| **Fair Value Measurements Of Financial Instruments [Line Items]**                                                                                              |          |          |          |
| Cash and due from banks                                                                                                                                        | 92,860        | 74,427        |          |
| Interest-bearing deposits                                                                                                                                      | 5,151         | 3,012         |          |
| Securities available for sale, at fair value                                                                                                                   | 1,347,611     | 1,318,365     |          |
| Other investments                                                                                                                                              | 44,077        | 35,444        |          |
| Loans                                                                                                                                                          | 4,334,214     | 4,283,833     |          |
| Deposits                                                                                                                                                       | 4,460,421     | 4,603,863     |          |
| Short-term borrowings                                                                                                                                          | 845,873       | 626,615       |          |
| Long-term debt                                                                                                                                                 | 136,672       | 144,385       |          |
| 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                                                                                                                                        | 92,860        | 74,427        |          |
| Interest-bearing deposits                                                                                                                                      | 5,151         | 3,012         |          |
| Securities available for sale, at fair value                                                                                                                   | 1,347,611     | 1,318,365     |          |
| Other investments                                                                                                                                              | 44,077        | 35,444        |          |
| Loans                                                                                                                                                          | 4,350,182     | 4,321,847     |          |
| Deposits                                                                                                                                                       | 4,465,990     | 4,531,685     |          |
| Short-term borrowings                                                                                                                                          | 845,862       | 626,603       |          |
| Long-term debt                                                                                                                                                 | 137,861       | 145,477       |          |
| Subordinated debt                                                                                                                                              | 61,755        | 51,706        |          |
| Estimate of Fair Value, Fair Value Disclosure [Member] | Level 1 [Member]                                                                                      |          |          |          |
| **Fair Value Measurements Of Financial Instruments [Line Items]**                                                                                              |          |          |          |
| Cash and due from banks                                                                                                                                        | 92,860        | 74,427        |          |
| Interest-bearing deposits                                                                                                                                      | 5,151         | 3,012         |          |
| Securities available for sale, at fair value                                                                                                                   | 0             | 0             |          |
| Other investments                                                                                                                                              | 0             | 0             |          |
| Loans                                                                                                                                                          | 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                                                                                                                   | 1,318,037     | 1,293,422     |          |
| Other investments                                                                                                                                              | 44,077        | 35,444        |          |
| Loans                                                                                                                                                          | 27,342        | 36,903        |          |
| Deposits                                                                                                                                                       | 4,465,990     | 4,531,685     |          |
| Short-term borrowings                                                                                                                                          | 845,862       | 626,603       |          |
| Long-term debt                                                                                                                                                 | 137,861       | 145,477       |          |
| 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                                                                                                                   | 29,574        | 24,943        |          |
| Other investments                                                                                                                                              | 0             | 0             |          |
| Loans                                                                                                                                                          | 4,322,840     | 4,284,944     |          |
| Deposits                                                                                                                                                       | 0             | 0             |          |
| Short-term borrowings                                                                                                                                          | 0             | 0             |          |
| Long-term debt                                                                                                                                                 | 0             | 0             |          |
| Subordinated debt                                                                                                                                              | $ 61,755      | $ 51,706      |          |

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