Supplemental Cash Flow Disclosures - Non-cash Investing and Financing Activities (Detail) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Supplemental Cash Flow Information [Abstract]
Real Estate Owned, Transfer to Real Estate Owned	$ 3,067	$ 4,824	$ 8,257
Cash paid during the year for:
Interest	21,552	19,208	15,818
Income taxes	27,902	19,950	8,331
Non-cash investing and financing activities:
Loans transferred to other real estate owned and repossessed assets	1,891	0	0
Fair value of loans transferred from held to maturity to available for sale	15,102	18,758	3,196
Gross (decrease) increase in market value adjustment to securities available for sale	1,983	(6,919)	2,949
Gross (decrease) increase in market value adjustment to derivatives	(783)	(549)	401
Investments committed to purchase, not settled	0	0	694
Noncash or Part Noncash Acquisition, Value of Assets Acquired	$ 37,070	$ (501,516)	$ 463
Other Significant Noncash Transaction, Consideration Received	245	437	0
Treasury stock reissued	$ 2,258	$ 0	$ 0
Other Significant Noncash Transaction, Value of Consideration Received	$ 0	$ 3,769	$ 0

Cash paid for interest and income taxes during the period.

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Credit Valuation Gain Loss on Derivative Asset Gross

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Gross increase (decrease) in market value adjustment to securities available for sale.

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Investments Committed to Purchase, Not Yet Paid

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Noncash Transactions, Stock Issued During Period, Value

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The amount of cash paid during the current period to foreign, federal, state, and local authorities as taxes on income, net of any cash received during the current period as refunds for the overpayment of taxes.

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Amount of cash paid for interest. Includes, but is not limited to, payment to settle zero-coupon bond attributable to accreted interest of debt discount and debt instrument with insignificant coupon interest rate in relation to effective interest rate of borrowing attributable to accreted interest of debt discount.

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The value of an asset or business acquired in a noncash (or part noncash) acquisition. Noncash is defined as information about all investing and financing activities of an enterprise during a period that affect recognized assets or liabilities but that do not result in cash receipts or cash payments in the period. "Part noncash" refers to that portion of the transaction not resulting in cash receipts or cash payments in the period.

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The noncash (or part noncash) consideration received in a transaction. Noncash is defined as transactions during a period that do not result in cash receipts or cash payments in the period. "Part noncash" refers to that portion of a transaction not resulting in cash receipts or cash payments in the period.

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Value of investments transferred from the entity's investments in noncash transactions.

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Value transferred out of real estate owned (REO) in noncash transactions.

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Value of loans and leases held in the entity's portfolio transferred to loans and leases held-for-sale in noncash transactions.

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Value transferred from mortgage loans to real estate owned (REO) in noncash transactions.

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