Non-employee Directors Annual Retainer, Amount Paid

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- Definition

Share-based Compensation BY Share-based Payment Award, Annual Retainer Convertible To Class A Common Stock, Percentage

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- Definition

Share-based Compensation Arrangement By Share-based Payment Award, Non-employee Directors Annual Retainer

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- Definition

Share-based Compensation Arrangement By Share-based Payment Award, Restriction Period

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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.

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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
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- Definition

The amount of expense, net of income tax, 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.

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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.

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- Definition

The difference between the maximum number of shares (or other type of equity) authorized for issuance under the plan (including the effects of amendments and adjustments), and the sum of: 1) the number of shares (or other type of equity) already issued upon exercise of options or other equity-based awards under the plan; and 2) shares (or other type of equity) reserved for issuance on granting of outstanding awards, net of cancellations and forfeitures, if applicable.

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- Definition

Gross number of shares (or other type of equity) issued during the period as a result of any equity-based compensation plan other than an employee stock ownership plan (ESOP). Shares issued could result from the issuance of restricted stock, the exercise of stock options, stock issued under employee stock purchase plans, and/or other employee benefit plans.

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Significant Accounting Policies (Stock-based Compensation and Other) (Details) - USD ($)	3 Months Ended	9 Months Ended	12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Dec. 31, 2018	Dec. 31, 2017
Schedule of Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Amount of directors, annual retainer paid in restricted shares			$ 90,000
Annual non-employee directors retainer amount			$ 150,000
Class A Common Stock \| Executives \| Stock Compensation Plan [Member]
Schedule of Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares issued during the year under the Company's stock compensation plans (shares)			96,153	92,572
Class A common stock available for issuance under the plan (shares)			311,275
Compensation expense related to share awards			$ 3,400,000	$ 3,500,000
Compensation expense related to share awards, net of tax			$ 2,700,000	2,300,000
Class A Common Stock \| Non-employee directors \| Stock Compensation Plan [Member]
Schedule of Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Class A common stock available for issuance under the plan (shares)			54,042
Compensation expense related to share awards			$ 900,000	900,000
Compensation expense related to share awards, net of tax			$ 700,000	$ 600,000
Class A Common Stock \| Non-employee directors \| Restricted stock
Schedule of Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares issued during the year under the Company's stock compensation plans (shares)			26,968	18,643
Amount of directors, annual retainer paid in restricted shares	$ 22,500	$ 66,750
Annual non-employee directors retainer amount	$ 37,500	$ 108,750		$ 37,500
Percentage of annual retainer that may be received in shares of Class A stock (percent)			100.00%
Class A Common Stock \| Non-employee directors \| Voluntary shares
Schedule of Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares issued during the year under the Company's stock compensation plans (shares)			560	2,746
Class A Common Stock \| Participant's Retirement Date \| Executives \| Stock Compensation Plan [Member]
Schedule of Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Duration of restrictions on stock assignment, pledges or transfers			5 years
Class A Common Stock \| Date of award \| Executives \| Stock Compensation Plan [Member]
Schedule of Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Duration of restrictions on stock assignment, pledges or transfers			5 years
Class A Common Stock \| Date of award \| Non-employee directors \| Stock Compensation Plan [Member]
Schedule of Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Duration of restrictions on stock assignment, pledges or transfers			10 years
Class A Common Stock \| Participants retirement from board of directors \| Non-employee directors \| Stock Compensation Plan [Member]
Schedule of Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Duration of restrictions on stock assignment, pledges or transfers			5 years
Class A Common Stock \| Minimum age of director upon retirement from board \| Non-employee directors \| Stock Compensation Plan [Member]
Schedule of Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Duration of restrictions on stock assignment, pledges or transfers			70 years
Maximum \| Class A Common Stock \| Date of award \| Executives \| Stock Compensation Plan [Member]
Schedule of Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Duration of restrictions on stock assignment, pledges or transfers			10 years
Minimum \| Class A Common Stock \| Date of award \| Executives \| Stock Compensation Plan [Member]
Schedule of Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Duration of restrictions on stock assignment, pledges or transfers			3 years