Date the equity-based award vests, in CCYY-MM-DD format.

No definition available.

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- Definition

Period which an executive's right to exercise an award is no longer contingent on satisfaction of either a service condition, market condition or a performance condition.

+ References

No definition available.

+ Details

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- Definition

Price of shares obligated to be repurchased expressed as a percentage of its book value

+ References

No definition available.

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- Definition

Period for distributing shares following the grant date of the shares.

+ References

No definition available.

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- References

No definition available.

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- Definition

Represents the expense recognized during the period arising from equity-based compensation arrangements (for example, shares of stock, unit, stock options or other equity instruments) with employees, directors and certain consultants qualifying for treatment as employees.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SAB Topic 14.F)
-URI http://asc.fasb.org/extlink&oid=27013229&loc=d3e301413-122809

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5047-113901

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (h)(1)(i)
-URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901

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Balance Type:	debit
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- Definition

The total fair value of shares issued during the period under a deferred compensation arrangement.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(2)
-URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901

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- Definition

Period which an employee's right to exercise an award is no longer contingent on satisfaction of either a service condition, market condition or a performance condition, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)(1)
-URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901

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- Definition

The number of grants made during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(2)(iii)(1)
-URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901

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- Definition

The weighted average fair value at grant date for nonvested equity-based awards issued during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(2)(iii)(1)
-URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901

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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.

+ Details

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- Definition

Number of share instruments newly issued under a share-based compensation plan.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901

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- Definition

The remaining number of shares authorized to be repurchased by an entity's Board of Directors under a stock repurchase plan.

+ References

No definition available.

+ Details

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Stock Based Compensation (Details) - USD ($) $ / shares in Units, $ in Thousands		12 Months Ended
	Feb. 08, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Class B [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares distribution period from grant date		1 year
Summary of stock Issuances [Abstract]
Period restricted stocks will vest ratably from date of grant		3 years
Class B [Member] \| 05/12/2015 [Member]
Summary of stock Issuances [Abstract]
Number of shares issued (in shares)		21,252
Vesting date		May 12, 2016
Period		7/1/2015 - 6/30/2016
Grant date fair value per share (in dollars per share)		$ 22.59
Class B [Member] \| 5/10/2016 [Member]
Summary of stock Issuances [Abstract]
Number of shares issued (in shares)		17,677
Vesting date		May 10, 2017
Period		7/1/2016 - 6/30/2017
Grant date fair value per share (in dollars per share)		$ 24.89
Class B [Member] \| 5/09/2017 [Member]
Summary of stock Issuances [Abstract]
Number of shares issued (in shares)		18,183
Vesting date		May 09, 2018
Period		7/1/2017 - 6/30/2018
Grant date fair value per share (in dollars per share)		$ 24.20
Class B [Member] \| 8/31/2017 [Member]
Summary of stock Issuances [Abstract]
Number of shares issued (in shares)		1,257
Vesting date		May 09, 2018
Period		8/31/2017 - 6/30/2018
Grant date fair value per share (in dollars per share)		$ 21.90
Class B [Member] \| Outside Director [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation cost charged against income		$ 454	$ 460	$ 460
Class B [Member] \| Executives [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares awarded (in shares)	20,181
Total value of shares issued	$ 480
Summary of stock Issuances [Abstract]
Grant date fair value per share (in dollars per share)	$ 23.80
1981 Stock Purchase Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Purchase price of shares obligated to be repurchased, percentage of book value		90.00%
1981 Stock Purchase Plan [Member] \| Class A [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of outstanding shares eligible for repurchase (in shares)		46,875
1981 Stock Purchase Plan [Member] \| Class B [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of outstanding shares eligible for repurchase (in shares)		187,500