Compensation and Benefit Plans - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Compensation And Benefit Plans Disclosure [Line Items]
Fair value of plan assets	$ 14,732	$ 15,038	$ 14,553
Employer contributions to 401(k) plan	$ 317	339
Maximum employer matching contribution percentage	4.00%
Number of ESOP shares purchased	723,751
Loan receivable - ESOP	$ 6,712
ESOP compensation expense after tax	526
Interest on ESOP loan	52
Employee Stock Ownership Plan
Compensation And Benefit Plans Disclosure [Line Items]
ESOP borrowed amount	$ 7,238
Number of ESOP shares purchased	723,751
ESOP shares purchased expressed as percentage of common stock sold in stock offering	3.92%
Expected period of loan repaid	15 years
Fair Value Measurements
Compensation And Benefit Plans Disclosure [Line Items]
Fair value of plan assets	$ 14,696	$ 15,296

Compensation and benefit plans disclosure line items.

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- Definition

ESOP shares purchased expressed as a percentage of common stock sold in the stock offering.

+ References

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- Definition

Employee stock ownership plan ESOP compensation expense after tax.

+ References

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- Definition

Employee stock ownership plan ESOP period for repayment of loan.

+ References

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- Definition

Loan receivable from ESOP.

+ References

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- Definition

Fair value of assets that have been segregated and restricted to provide pension or postretirement benefits. Assets include, but are not limited to, stocks, bonds, other investments, earnings from investments, and contributions by the employer and employees.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920

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- Definition

Amount of discretionary contributions made by an employer to a defined contribution plan.

+ References

No definition available.

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- Definition

Percentage of employees' gross pay for which the employer contributes a matching contribution to a defined contribution plan.

+ References

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- Definition

An entity often discloses the amount of interest paid by the ESOP to a lender.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 40
-Section 25
-Paragraph 9
-Subparagraph (a),(b)
-URI http://asc.fasb.org/extlink&oid=65888597&loc=d3e16545-113920

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- Definition

An entity will typically disclose the amount of any repurchase obligation.

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 40
-Section 50
-Paragraph 1
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- Definition

Number of shares of capital stock issued (purchased by employees) in connection with an employee stock ownership plan.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
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-Name Accounting Standards Codification
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-SubTopic 10
-Section S99
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