Commitments And Contingencies - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Loss Contingencies [Line Items]
Securities available for sale, mortgaged-related securities, pledged	$ 1,263,227
Securities held to maturity, mortgaged related securities, pledged	1,600,000	$ 346,700
Securities available for sale, other securities, pledged	346,000
Loans pledged to FHLB, collateral for wholesale borrowings	30,100,000	29,400,000
Commitments	2,274,678
Rental expense under non-cancelable operating lease and license agreements	33,200	32,600	$ 32,800
Rental income on bank-owned properties, netted in occupancy and equipment expense	9,500	7,100	$ 3,700
GNMA Securities
Loss Contingencies [Line Items]
Purchase commitments	29,400
Total loans
Loss Contingencies [Line Items]
Commitments	1,935,275	2,100,000
Commercial, performance stand-by, and financial stand-by letters of credit
Loss Contingencies [Line Items]
Commitments	$ 339,403	$ 324,300

Fair value portion of arrangements with third parties, including, but not limited to, operating lease arrangement and arrangement in which the entity has agreed to expend funds to procure goods or services, or has agreed to commit resources to supply goods or services.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(25))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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The carrying amount as of the date of the latest financial statement presented of mortgage-related securities classified as available for sale or held for investment which are owned but transferred to another party to serve as collateral to partially or fully secure a debt obligation, repurchase agreement or other current or potential obligation, and for which the transferee does not have the right by contract or custom to sell or re-pledge them to an unrelated party.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 30
-Section 50
-Paragraph 1A
-Subparagraph (b)(1)(i)
-URI http://asc.fasb.org/extlink&oid=64858031&loc=SL6224234-111729

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Minimum amount to be expended to satisfy the terms of arrangements in which the entity has agreed to expend funds to procure goods or services, excluding long-term purchase commitments or unconditional purchase obligations.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
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Reference 2: http://www.xbrl.org/2003/role/presentationRef
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-Name Accounting Standards Codification
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Income earned by providing the use of assets to an outside party in exchange for a payment or series of payments that is nonoperating in nature.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
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-Name Accounting Standards Codification
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-Section S99
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