Minimum age for employee participation.

No definition available.

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- Definition

Minimum service period for employees participation.

+ 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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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
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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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- 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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Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
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Period Type:	duration

- Definition

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

+ References

No definition available.

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Details

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- Details

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Namespace Prefix:
Data Type:	na
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Period Type:

- Details

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Retirement Plans - Additional Information (Detail) - USD ($)	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2018	Dec. 31, 2017
Defined Benefit Plan Disclosure [Line Items]
Deferred compensation obligations	$ 6,932,000		$ 6,932,000			$ 6,605,000
401(k) Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Minimum age for employees			21 years
Minimum period for employees to participate			90 days
Discretionary matching contribution equal to percentage of participant's contribution			50.00%
Discretionary matching contribution maximum percentage of eligible compensation			4.00%
Employer's contribution to retirement plan	$ 247,000	$ 192,000	$ 446,000	$ 371,000
Supplemental Retirement Plans [Member] \| Scenario, Forecast [Member]
Defined Benefit Plan Disclosure [Line Items]
Employer's contribution to retirement plan					$ 1,106,000