Deferred compensation arrangements non interest expense.

No definition available.

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- Definition

Employee service period under ESOP.

+ References

No definition available.

+ Details

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- Definition

Aggregate carrying value as of the balance sheet date of the liabilities for all deferred compensation arrangements. Represents currently earned compensation under compensation arrangements that is not actually paid until a later date.

+ References

No definition available.

+ Details

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Period Type:	instant

- Definition

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.

+ References

No definition available.

+ Details

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- Definition

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

+ References

No definition available.

+ Details

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- Definition

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

+ References

No definition available.

+ Details

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- Definition

Percentage employer matches of the employee's percentage contribution matched.

+ References

No definition available.

+ Details

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- Definition

This item represents the amount of cash contributions during the period made by the entity to the Employee Stock Ownership Plan (ESOP).

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 40
-Section 50
-Paragraph 1
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=65895303&loc=d3e17540-113929

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Data Type:	xbrli:monetaryItemType
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Period Type:	duration

- Definition

The aggregate amount of expenditures for salaries, wages, profit sharing and incentive compensation, and other employee benefits, including equity-based compensation, and pension and other postretirement benefit expense.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 225
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03.4)
-URI http://asc.fasb.org/extlink&oid=63488584&loc=d3e20235-122688

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Balance Type:	debit
Period Type:	duration

- Details

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- Details

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Retirement Plans - Additional Information (Detail) - USD ($)	3 Months Ended		12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017
Defined Benefit Plan Disclosure [Line Items]
Salaries & benefits expense	$ 21,652,000	$ 20,893,000
Employee service period under ESOP	1 year
Contribution and paid out as benefits under ESOP	$ 465,000	525,000
Deferred compensation obligations	6,809,000			$ 6,605,000
Earnings credits on deferred balances included in noninterest expense	$ 124,000	145,000
401(k) Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Discretionary matching contribution equal to percentage of participant's contribution	50.00%
Discretionary matching contribution maximum percentage of eligible compensation	4.00%
Salaries & benefits expense	$ 203,000	186,000
Employer's contribution to retirement plan	199,000	179,000
Supplemental Retirement Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Employer's contribution to retirement plan	$ 267,000	$ 259,000
Supplemental Retirement Plans [Member] \| Scenario, Forecast [Member]
Defined Benefit Plan Disclosure [Line Items]
Employer's contribution to retirement plan			$ 1,106,000