Commitments and Contingencies - Summary of Financial Instruments with Off-Balance Sheet Risk (Detail) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Commitments to sell loans	$ 58,897	$ 57,405
Standby letters of credit
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Financial instruments with off-balance sheet risk	316,941	250,536
Commercial letters of credit
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Commercial letters of credit	3,100	2,115
Commitments under commercial loans and lines of credit \| Commitments under commercial loans and lines of credit
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Financial instruments with off-balance sheet risk	5,164,186	3,401,653
Home equity and other revolving lines of credit \| Unused lines of credit
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Financial instruments with off-balance sheet risk	1,178,306	1,006,329
Outstanding residential mortgage loan commitments \| Outstanding residential mortgage loan commitments
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Financial instruments with off-balance sheet risk	235,310	192,685
Commitments under unused lines of credit—credit card \| Unused lines of credit
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Financial instruments with off-balance sheet risk	$ 66,229	$ 54,906

The fair value of financial liabilities, which are not recognized in the financial statements (off-balance sheet) because they fail to meet some other criterion for recognition.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 10
-URI http://asc.fasb.org/extlink&oid=109250915&loc=d3e13433-108611

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+ References

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- Definition

The total amount of the contingent obligation under letters of credit outstanding as of the reporting date.

+ References

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Reflects the carrying amount of loans and leases for which agreements to acquire or dispose exist.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 825
-Section 50
-Paragraph 1
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=108315417&loc=d3e61044-112788

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-Section 50
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=108315417&loc=d3e61082-112788

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