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Stock-Based Compensation - Stock Options (Parenthetical) (Detail) - shares shares in Thousands | Dec. 31, 2017 | Dec. 31, 2016
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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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- 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 + Details
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