Savings and Retirement Plans (Details) - 401(K) and Deferred Compensation Plan - USD ($)	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Deferred Compensation Arrangement with Individual, Postretirement Benefits [Line Items]
401(k) Maximum annual contribution per employee	$ 18,500	$ 18,000	$ 18,000
401(k) Employer match	50.00%	50.00%	50.00%
401(k) Employer contribution expense	$ 688,000	$ 632,000	$ 602,000
Deferred compensation liability to participants	$ 12,000,000	$ 12,800,000
Maximum
Deferred Compensation Arrangement with Individual, Postretirement Benefits [Line Items]
401(k) Maximum of employer match as a percentage of employee eligible earnings	5.00%	5.00%	5.00%

Deferred Compensation Arrangement with Individual, Employer Contribution Per Employee, Matching Percent

No definition available.

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- Definition

Amount of contributions made by employer into fund established for purposes of making future disbursement to individual in accordance with deferred compensation arrangement.

+ References

No definition available.

+ Details

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- 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.

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- Definition

The carrying amount of the liability as of the balance sheet date to an individual under a deferred compensation arrangement. This amount may be the result of periodic accruals made over the period of active employment, or reflect termination benefits resulting contractual terms or a death benefit.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 710
-SubTopic 10
-Section 30
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6409875&loc=d3e20015-108363

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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

Maximum amount the employee may contribute to a defined contribution plan.

+ References

No definition available.

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