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Earnings Per Share - Additional Information (Detail) - shares | 12 Months Ended
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Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
Earnings Per Share [Line Items] |  |  |
Convertible Class B common stock outstanding | 2,601,996 | 2,711,811 | 2,699,710
Anti-dilutive stock options excluded from earnings per share | 11,664 | 31,839 | 67,014

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- Definition Securities (including those issuable pursuant to contingent stock agreements) that could potentially dilute basic earnings per share (EPS) or earnings per unit (EPU) in the future that were not included in the computation of diluted EPS or EPU because to do so would increase EPS or EPU amounts or decrease loss per share or unit amounts for the period presented. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 260 -SubTopic 10 -Section 50 -Paragraph 1 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=6371337&loc=d3e3550-109257 + Details
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- Definition Class B common stock securities that may be converted to Common stock securities at any time on a one-for-one basis at the option of the shareholder. + References No definition available. + Details
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Balance Type: | na
Period Type: | instant

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- Definition Earnings per share disclosures. + References No definition available. + Details
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