Analysis of Contractual Maturities of Outstanding Repurchase Agreements (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Amount
Repurchase agreements	$ 800,000	$ 500,000
Weighted Average Interest Rate
Contractual Maturity Over 90 days, Weighted Average Interest Rate	2.24%
Contractual Maturity
Amount
2028	$ 300,000
2029	500,000
Repurchase agreements	$ 800,000
Weighted Average Interest Rate
2028	2.37%
2029	2.16%
Contractual Maturity Over 90 days, Weighted Average Interest Rate	2.24%
Earlier of Contractual Maturity or Next Call Date
Amount
2021	$ 400,000
2022	400,000
Repurchase agreements	$ 800,000
Weighted Average Interest Rate
2021	2.31%
2022	2.16%
Contractual Maturity Over 90 days, Weighted Average Interest Rate	2.24%

Securities Sold under Agreements to Repurchase, Maturities Summary [Abstract]

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Amount of cash received as security in return for loaning securities to another party which are due within one year of the Balance Sheet date.

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Amount of cash received as security in return for loaning securities to another party which are due within three year of the Balance Sheet date.

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Securities Sold Under Agreements To Repurchase Maturities Summary Due Within Two Years Of Balance Sheet Date

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The weighted average interest rate applicable to the cash received as security in return for loaning securities to another party which are due from eight to nine years of the Balance Sheet date.

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Securities Sold under Agreements to Repurchase, Maturities Summary, Weighted Average Interest Rate of Amounts Due [Abstract]

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The weighted average interest rate applicable to the cash received as security in return for loaning securities to another party which are due within one year of the Balance Sheet date.

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The weighted average interest rate applicable to the cash received as security in return for loaning securities to another party which are due from one to two years of the Balance Sheet date.

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The weighted average interest rate applicable to the cash received as security in return for loaning securities to another party which are due from twp to three years of the Balance Sheet date.

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Securities Sold Under AgreementsTo Repurchase Maturities Summary Due With in Four Years Of Balance Sheet Date.

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Interest rate on the amount to be repaid to the counterparty to the repurchase agreement when the carrying amount (or market value, if higher than the carrying amount) of securities or other assets sold under the repurchase agreement exceeds 10 percent of total assets.

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Amount, after the effects of master netting arrangements, of funds outstanding borrowed in the form of a security repurchase agreement between the entity and another party for the sale and repurchase of identical or substantially the same securities at a date certain for a specified price. Includes liabilities not subject to a master netting arrangement and not elected to be offset.

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