Securities - Additional Information (Detail) $ in Thousands	3 Months Ended
Mar. 31, 2021 USD ($) Holding	Mar. 31, 2020 USD ($)	Dec. 31, 2020 USD ($) Holding
Schedule Of Available For Sale Securities And Held To Maturity [Line Items]
Maximum percentage of equity of one issuer	10.00%
Number of holdings greater than specified percentage of equity \| Holding	0		0
Equities securities	$ 13,123		$ 13,047
Securities with an aggregate fair value	1,800,000		1,800,000
Proceeds from sale of available-for-sale securities	0	$ 222,668
Net unrealized gains on available-for-sale securities included in AOCI	24,800		46,900
Accrued interest receivable	68,896		66,790
Federal home loan bank stock, Total	29,300		34,000
Us Government Securities and Mortgage Backed and Collateralized Securities Issued By Direct Governmental Entity or Government-Sponsored Entity [Member]
Schedule Of Available For Sale Securities And Held To Maturity [Line Items]
Estimated credit losses	0
Held-to-maturity Securities [Member]
Schedule Of Available For Sale Securities And Held To Maturity [Line Items]
Accrued interest receivable	6,300		$ 5,300
Grantor Trusts [Member]
Schedule Of Available For Sale Securities And Held To Maturity [Line Items]
Equities securities	$ 10,100

Amount, after tax, of accumulated unrealized gain (loss) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section 45
-Paragraph 14
-URI http://asc.fasb.org/extlink&oid=121641772&loc=d3e681-108580

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Amount of expense (reversal of expense) for expected credit loss on investment in debt security measured at amortized cost (held-to-maturity).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 50
-Paragraph 13
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Amount of investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI).

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-Publisher FASB
-Name Accounting Standards Codification
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-Section 45
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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).

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 325
-Section 45
-Paragraph 1
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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.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
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The carrying amount, as of the date of the latest financial statement presented, of other assets which are owned but transferred to serve as collateral for the payment of the related debt obligation, primarily a secured borrowing or repurchase agreement, and for which the transferee is not permitted to sell or re-pledge them to an unrelated party.

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The cash inflow associated with the sale of debt and equity securities classified as available-for-sale securities.

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The maximum percentage of shareholders' equity of any one issuer other than the U.S. government and its agencies.

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Schedule of available for sale securities and held to maturity.

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