Fair Value Disclosures - Schedule of Estimated Fair Values and Carrying Values of All Financial Instruments (Detail) - USD ($) $ in Thousands	Jun. 30, 2016	Dec. 31, 2015	Jun. 30, 2015
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
CASH AND DUE FROM BANKS	$ 135,092	$ 179,140	$ 149,524
FEDERAL FUNDS SOLD	2,960	3,810	5,720
INTEREST-BEARING DEPOSITS IN BANKS	67,746	89,936	18,179
INTEREST-BEARING TIME DEPOSITS IN BANKS	2,427	3,495	5,456
Available-for-sale Securities	2,795,356	2,733,899	2,729,113
Held-to-maturity securities	137	278	295
Loans	3,264,328	3,308,716	2,928,769
SHORT-TERM BORROWINGS	556,924	615,675	621,155
Carrying Value [Member] \| Level 1 Inputs [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
CASH AND DUE FROM BANKS	135,092	179,140	149,524
FEDERAL FUNDS SOLD	2,960	3,810	5,720
INTEREST-BEARING DEPOSITS IN BANKS	67,746	89,936	18,179
Deposits with no stated maturities	4,501,536	4,569,317	4,129,015
Carrying Value [Member] \| Level 2 Inputs [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
INTEREST-BEARING TIME DEPOSITS IN BANKS	2,427	3,495	5,456
Held-to-maturity securities	137	278	295
Accrued interest receivable	33,516	34,697	32,003
Deposits with stated maturities	554,753	620,852	598,404
SHORT-TERM BORROWINGS	556,924	615,675	621,155
Accrued interest payable	283	240	242
Carrying Value [Member] \| Levels 1 and 2 Inputs [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available-for-sale Securities	2,795,356	2,733,899	2,729,113
Carrying Value [Member] \| Level 3 Inputs [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans	3,264,328	3,308,716	2,928,769
Estimated Fair Value [Member] \| Level 1 Inputs [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
CASH AND DUE FROM BANKS	135,092	179,140	149,524
FEDERAL FUNDS SOLD	2,960	3,810	5,720
INTEREST-BEARING DEPOSITS IN BANKS	67,746	89,936	18,179
Deposits with no stated maturities	4,501,536	4,569,317	4,129,015
Estimated Fair Value [Member] \| Level 2 Inputs [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
INTEREST-BEARING TIME DEPOSITS IN BANKS	2,429	3,500	5,466
Held-to-maturity securities	141	283	301
Accrued interest receivable	33,516	34,697	32,003
Deposits with stated maturities	556,224	622,572	600,093
SHORT-TERM BORROWINGS	556,924	615,675	621,155
Accrued interest payable	283	240	242
Estimated Fair Value [Member] \| Levels 1 and 2 Inputs [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available-for-sale Securities	2,795,356	2,733,899	2,729,113
Estimated Fair Value [Member] \| Level 3 Inputs [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans	$ 3,269,221	$ 3,316,243	$ 2,935,344

Accrued interest payable.

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Deposits with no stated maturities.

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Deposits with stated maturities.

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Interest-bearing time deposits in banks.

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Amount of debt 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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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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The amount outstanding of funds lent to other depository institutions, securities brokers, or securities dealers in the form of Federal Funds sold; for example, immediately available funds lent under agreements or contracts that mature in one business day or roll over under a continuing contract, regardless of the nature of the transaction or the collateral involved, excluding overnight lending for commercial and industrial purposes. Also include Federal Funds sold under agreements to resell on a gross basis, excluding (1) sales of term Federal Funds, (2) due bills representing purchases of securities or other assets by the reporting bank that have not yet been delivered and similar instruments, (3) resale agreements that mature in more than one business day involving assets other than securities, and (4) yield maintenance dollar repurchase agreements.

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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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Carrying amount as of the balance sheet date of interest earned but not received. Also called accrued interest or accrued interest receivable.

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Amount after allowance and 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. Includes loans held for sale. Excludes loans and leases covered under loss sharing agreements.

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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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