Borrowings - Concerning of Other Borrowings (Detail) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016
Debt Instrument [Line Items]
Other borrowings	$ 11,409	$ 12,385
Fixed Rate Borrowing [Member]
Debt Instrument [Line Items]
Maturity date Range, From	Dec. 20, 2017
Maturity date Range, To	Dec. 21, 2017
Weighted Average Interest Rate	3.61%
Other borrowings		10,000
Fixed Rate Borrowing [Member] \| Minimum [Member]
Debt Instrument [Line Items]
Stated Interest Rate Range	3.48%
Fixed Rate Borrowing [Member] \| Maximum [Member]
Debt Instrument [Line Items]
Stated Interest Rate Range	3.73%
Fixed Rate Amortizing Borrowing [Member]
Debt Instrument [Line Items]
Maturity date Range, From	Apr. 01, 2024
Maturity date Range, To	Jun. 01, 2037
Weighted Average Interest Rate	1.86%
Other borrowings	$ 11,409	$ 2,385
Fixed Rate Amortizing Borrowing [Member] \| Minimum [Member]
Debt Instrument [Line Items]
Stated Interest Rate Range	1.16%
Fixed Rate Amortizing Borrowing [Member] \| Maximum [Member]
Debt Instrument [Line Items]
Stated Interest Rate Range	2.01%

Contractual interest rate for funds borrowed, under the debt agreement.

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

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+ References

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Latest date the outstanding debt instruments are required to be repaid, in CCYY-MM-DD format.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-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

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Earliest date the outstanding debt instruments are required to be repaid, in CCYY-MM-DD format.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-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

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Weighted average interest rate of debt outstanding.

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- Definition

The noncurrent portion of Federal Home Loan Bank borrowings initially due beyond one year or beyond the normal operating cycle if longer.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 10
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6802200&loc=d3e1835-112601

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03(a)(16)(a)(2))
-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

Reference 3: http://www.xbrl.org/2003/role/presentationRef
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-Name Accounting Standards Codification
-Topic 440
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