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Stockholders Equity - Additional Information (Detail) $ / shares in Units, $ in Millions |  |  | 12 Months Ended
--- | --- | --- | ---
Oct. 05, 2016 | Sep. 07, 2016 | Dec. 31, 2017 USD ($) $ / shares shares | Dec. 31, 2016 USD ($) $ / shares shares | Dec. 31, 2015 USD ($) $ / shares shares
Stockholders Equity [Line Items] |  |  |  |  |
Preferred stock, shares authorized |  |  | 3,000,000 |  |
Preferred stock, par value | $ / shares |  |  | $ 1 |  |
Common Stock, shares authorized |  |  | 240,000,000 |  |
Common stock, par value | $ / shares |  |  | $ 1 |  |
Dividends paid | $ / shares |  |  | $ 0.56 | $ 0.48 | $ 0.38
Stock split ratio | 2 | 2 |  |  |
Stock repurchase program number of shares authorized to repurchase |  |  |  | 3,000,000 | 4,000,000
Shares repurchased |  |  | 2,533,350 | 3,273,109 | 3,816,474
Shares repurchased, value | $ |  |  | $ 139.1 | $ 135.2 | $ 128.1
Remaining authorization stock repurchase |  |  | 2,373,053 |  |
Common Class A |  |  |  |  |
Stockholders Equity [Line Items] |  |  |  |  |
Common Stock, shares authorized |  |  | 27,000,000 |  |
Common stock, par value | $ / shares |  |  | $ 5 |  |
Shares converted into Common Stock |  |  | 73,792 | 60,045 | 67,544
Treasury stock, number of shares held |  |  | 130,380 | 130,380 |
Common Stock |  |  |  |  |
Stockholders Equity [Line Items] |  |  |  |  |
Treasury stock, number of shares held |  |  | 18,914,082 | 17,135,628 |

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- Definition Aggregate dividends paid during the period for each share of common stock outstanding. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 505 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.3-04) -URI http://asc.fasb.org/extlink&oid=27012166&loc=d3e187085-122770 + Details
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- Definition Face amount or stated value per share of common stock. + 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(29)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
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- Definition The maximum number of common shares 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(29)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
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- Definition The number of shares converted in a noncash (or part noncash) transaction. Noncash is defined as transactions during a period that do not result in cash receipts or cash payments in the period. "Part noncash" refers to that portion of the transaction not resulting in cash receipts or cash payments in the period. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 50 -Paragraph 5 -URI http://asc.fasb.org/extlink&oid=98513485&loc=d3e4332-108586 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 50 -Paragraph 3 -URI http://asc.fasb.org/extlink&oid=98513485&loc=d3e4304-108586 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 50 -Paragraph 4 -URI http://asc.fasb.org/extlink&oid=98513485&loc=d3e4313-108586 + Details
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