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Investment Securities - Proceeds from Sale, Gross Gains (Losses) Realized on Sales, Maturities and Other-Than-Temporary Impairment Charges Related to Securities Available for Sale (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Gain (Loss) on Securities [Line Items]
Proceeds from sale	$ 15,939	$ 143,660	$ 55,744
Net gains (losses) and impairment	8,102	5,040	617
Calls And Maturities [Member]
Gain (Loss) on Securities [Line Items]
Gross losses	0	(60)	0
Gross gains	3,383	5,057	589
Other-than-temporary impairment	0	0	0
Total gain (losses) maturities and impairment	3,383	4,997	589
Sales [Member]
Gain (Loss) on Securities [Line Items]
Gross losses	0	(316)	(277)
Available-for-sale Securities, Gross Realized Losses	4,719	359	305
Total gain (losses) from sales transactions	$ 4,719	$ 43	$ 28

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Gain losses maturities and impairment.

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Net gains and impairment.

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Other-than-temporary impairment.

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This item represents the gross profit realized on the sale of debt or equity securities categorized neither as held-to-maturity nor trading securities.

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This item represents the gross loss realized on the sale of debt or equity securities categorized neither as held-to-maturity nor trading securities.

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This item represents the difference between the gross realized gains and losses realized on the sale of debt or equity securities categorized neither as held-to-maturity nor trading securities.

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Amount of cash inflow from sale of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 45
-Paragraph 11
-URI http://asc.fasb.org/extlink&oid=109979856&loc=d3e26853-111562

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 11
-URI http://asc.fasb.org/extlink&oid=109223946&loc=d3e3151-108585

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-URI http://asc.fasb.org/extlink&oid=109223946&loc=d3e3179-108585

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