Shareholders' Equity (Narrative) (Details) - $ / shares shares in Millions	Dec. 31, 2018	Dec. 31, 2017
Common Class A [Member]
Class of Stock [Line Items]
Common Stock, par value per share	$ 0.001	$ 0.001
Common Stock reserved for the conversion of Class B Common Stock and the exercise of stock options	3.3
Number of shares authorized to be repurchased	2.0
Common Class B [Member]
Class of Stock [Line Items]
Common Stock, par value per share	$ 0.001	$ 0.001

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.

No definition available.

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- Definition

Aggregate number of common shares reserved for future issuance.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.29)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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- Definition

Face amount or stated value per share of common stock.

+ References

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
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-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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- Definition

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

+ References

No definition available.

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