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Premises and Equipment, Net and Other Assets - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Property Plant And Equipment [Abstract]
Percentage of equity investment	50.00%
Low income housing tax credit investments	$ 18.5	$ 16.9
Tax credits and other tax benefits recognized from LIHTC investments	5.4	4.4	$ 4.2
Amortization expense resulting from LIHTC investments	4.4	$ 3.5	$ 2.9
Unfunded commitment on investments	$ 17.3

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Percentage of equity investment.

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Amount of affordable housing tax credits and other tax benefits recognized.

+ References

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 323
-SubTopic 740
-Section 50
-Paragraph 2
-Subparagraph (a)
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Amount of investment in qualified affordable housing projects.

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Amount of amortization expense of investment in qualified affordable housing projects.

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Amount of commitment or contingent commitments to qualified affordable housing project investments.

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-Name Accounting Standards Codification
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-SubTopic 740
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