Fair Values of Assets and Liabilities - Carrying Amounts and Fair Values of Financial Instruments (Detail) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017	Sep. 30, 2017
Fair Value Measurements Of Financial Instruments [Line Items]
Cash and due from banks	$ 93,162	$ 98,624
Interest-bearing deposits	3,022	8,668
Securities available for sale, at fair value	889,056	731,358
Debt Securities, Held-to-maturity	389,621	422,096
Other investments	25,029	29,837
Loans and Leases Receivable, Net of Deferred Income	5,662,782	5,407,376	$ 5,375,847
Deposits	5,895,143	5,580,705
Short-term borrowings	587,806	707,466
Subordinated debt	170,249	72,167
Long-term debt	7,706	8,161
Capital Lease Obligations	7,311	7,590
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	887,386	706,042
Other investments	25,029	29,837
Level 3 [Member]
Fair Value Measurements Of Financial Instruments [Line Items]
Securities available for sale, at fair value	1,670	25,316
Other investments	0	0
Carrying Amount [Member]
Fair Value Measurements Of Financial Instruments [Line Items]
Cash and due from banks	93,162	98,624
Interest-bearing deposits	3,022	8,668
Securities available for sale, at fair value	889,056	731,358
Debt Securities, Held-to-maturity	389,621	422,096
Other investments	25,029
Loans Held for sale, Amount	8,287	14,850
Loans and Leases Receivable, Net of Deferred Income	5,662,782	5,407,376
Deposits	5,895,143	5,580,705
Short-term borrowings	587,806	707,466
Subordinated debt	170,249	72,167
Long-term debt	7,706	8,161
Capital Lease Obligations	7,311	7,590
Estimate of Fair Value Measurement [Member]
Fair Value Measurements Of Financial Instruments [Line Items]
Cash and due from banks	93,162	98,624
Interest-bearing deposits	3,022	8,668
Securities available for sale, at fair value	889,056	731,358
Debt Securities, Held-to-maturity	373,933	418,249
Other investments	25,029	29,837
Loans Held for sale, Amount	8,287	14,850
Loans and Leases Receivable, Net of Deferred Income	5,643,537	5,443,434
Deposits	5,894,839	5,580,812
Short-term borrowings	587,776	707,263
Subordinated debt	173,533	65,785
Long-term debt	7,781	8,548
Capital Lease Obligations	7,311	7,590
Estimate of Fair Value Measurement [Member] \| Level 1 [Member]
Fair Value Measurements Of Financial Instruments [Line Items]
Cash and due from banks	93,162	98,624
Interest-bearing deposits	3,022	8,668
Securities available for sale, at fair value	0	0
Debt Securities, Held-to-maturity	0	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
Subordinated debt	0	0
Long-term debt	0	0
Capital Lease Obligations	0	0
Estimate of Fair Value Measurement [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	887,386	706,042
Debt Securities, Held-to-maturity	373,933	418,249
Other investments	25,029	29,837
Loans Held for sale, Amount	8,287	14,850
Loans and Leases Receivable, Net of Deferred Income	14,940	23,249
Deposits	5,894,839	5,580,812
Short-term borrowings	587,776	707,263
Subordinated debt	0	0
Long-term debt	7,781	8,548
Capital Lease Obligations	7,311	7,590
Estimate of Fair Value Measurement [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	1,670	25,316
Debt Securities, Held-to-maturity	0	0
Other investments	0	0
Loans Held for sale, Amount	0	0
Loans and Leases Receivable, Net of Deferred Income	5,628,597	5,420,185
Deposits	0	0
Short-term borrowings	0	0
Subordinated debt	173,533	65,785
Long-term debt	0	0
Capital Lease Obligations	$ 0	$ 0

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

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Amount equal to the present value (the principal) at the beginning of the lease term of minimum lease payments during the lease term (excluding that portion of the payments representing executory costs such as insurance, maintenance, and taxes to be paid by the lessor, together with any profit thereon) net of payments or other amounts applied to the principal through the balance sheet date.

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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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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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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 of investment in debt security measured at amortized cost (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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Amount of long-term debt classified as other.

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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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