Other Borrowings - Summary of Balances of Other Borrowings (Parenthetical) (Detail)	6 Months Ended	12 Months Ended
Jun. 30, 2018	Dec. 31, 2017
2.05% Fixed Rate FHLB Collateralized Borrowings [Member]
Debt Instrument [Line Items]
Collateralized borrowing, fixed rate	2.05%
Collateralized borrowing, maturity date	Jul. 02, 2018
1.38% Fixed Rate FHLB Collateralized Borrowings [Member]
Debt Instrument [Line Items]
Collateralized borrowing, fixed rate		1.38%
Collateralized borrowing, maturity date		Jan. 02, 2018
0.05% Fixed Rate Collateralized Borrowings [Member]
Debt Instrument [Line Items]
Collateralized borrowing, fixed rate	0.05%	0.05%
Collateralized borrowing, maturity date	Jul. 02, 2018	Jan. 02, 2018

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.

No definition available.

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- Definition

Date when the debt instrument is scheduled to be fully repaid, in CCYY-MM-DD format.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.22(a)(2))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (bbb)(2)
-URI http://asc.fasb.org/extlink&oid=99377789&loc=d3e19207-110258

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- Definition

Discloses the single interest rate [if] applicable to the advances from the Federal Home Loan Bank, by branch, as of the Balance Sheet date.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 470
-Section 50
-Paragraph 3
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=75038535&loc=d3e64711-112823

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 470
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6479118&loc=d3e64650-112822

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