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Capital Structure - Additional Information (Detail) - shares | 12 Months Ended |
--- | --- | ---
Dec. 31, 2017 | Dec. 31, 2016
Class of Stock [Line Items] |  |
Preferred stock, shares authorized | 2,000,000 | 2,000,000
Class B Common Stock [Member] |  |
Class of Stock [Line Items] |  |
Common stock, rights to vote | 84 |
Class A Common Stock [Member] |  |
Class of Stock [Line Items] |  |
Common stock, rights to vote | one |

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- Definition Description of voting rights of common stock. Includes eligibility to vote and votes per share owned. Include also, if any, unusual voting rights. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 505 -SubTopic 10 -Section 50 -Paragraph 3 -URI http://asc.fasb.org/extlink&oid=84159872&loc=d3e21475-112644 + Details
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- Definition The maximum number of nonredeemable preferred shares (or preferred stock redeemable solely at the option of the issuer) permitted to be issued by an entity's charter and bylaws. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02(28)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
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