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Minimum Regulatory Capital Requirements - Additional Information (Detail)	Jan. 01, 2019	Dec. 31, 2016	Dec. 31, 2015
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Minimum ratio of capital to risk-weighted assets		8.00%	8.00%
Minimum leverage ratio calculated as ratio of Tier 1 capital to average quarterly assets		11.77%	11.91%
Scenario, Forecast [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Capital conservation buffer	2.50%
Minimum ratio of capital to risk-weighted assets including capital conservation buffer	10.50%
Minimum ratio of capital to risk-weighted assets	8.00%
Minimum leverage ratio calculated as ratio of Tier 1 capital to average quarterly assets	4.00%
Capital conservation buffer at base level	0.625%
Regulatory capital requirements phase period	4 years
Scenario, Forecast [Member] | Common Equity Tier 1 Capital [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Minimum ratio of capital to risk-weighted assets	4.50%
Capital conservation buffer	2.50%
Minimum ratio of capital to risk-weighted assets including capital conservation buffer	7.00%
Scenario, Forecast [Member] | Tier 1 Capital [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Minimum ratio of capital to risk-weighted assets	6.00%
Minimum ratio of capital to risk-weighted assets including capital conservation buffer	8.50%

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- Definition

Capital Required For Capital Adequacy To Risk Weighted Asset

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Capital required for capital adequacy to risk weighted assets including capital conservation buffer.

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Regulatory capital requirements phase period.

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Risk weighted assets capital conservation buffer.

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Risk weighted assets capital conservation buffer at base level.

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- Definition

The minimum Total risk based capital ratio (total capital divided by risk weighted assets) required for capital adequacy purposes under the regulatory framework for prompt corrective action.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 505
-Section 50
-Paragraph 1
-Subparagraph (c)(1)
-URI http://asc.fasb.org/extlink&oid=35709795&loc=SL5958568-112826

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 505
-Section 50
-Paragraph 1H
-Subparagraph (c)(2)
-URI http://asc.fasb.org/extlink&oid=35709795&loc=d3e65071-112826

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 505
-Section 50
-Paragraph 1B
-URI http://asc.fasb.org/extlink&oid=35709795&loc=SL5958570-112826

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Tier 1 Leverage Capital divided by average assets as defined in the regulations.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 505
-Section 50
-Paragraph 1
-Subparagraph (c)(1)
-URI http://asc.fasb.org/extlink&oid=35709795&loc=SL5958568-112826

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-Publisher FASB
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-URI http://asc.fasb.org/extlink&oid=35709795&loc=d3e65071-112826

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