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Stock-Based Compensation - Stock Options (Parenthetical) (Detail) - shares shares in Thousands	Dec. 31, 2017	Dec. 31, 2016
Class A common stock
Stock-Based Compensation
Options to purchase stock	1,780	389
Class B common stock
Stock-Based Compensation
Options to purchase stock	2,965	5,040

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+ References

No definition available.

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- Definition

Number of options outstanding, including both vested and non-vested options.

+ 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

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

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