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Common Stock and Treasury Stock - Additional Information (Detail) - USD ($) | 3 Months Ended | 67 Months Ended |
--- | --- | --- | ---
Mar. 31, 2018 | Mar. 31, 2018 | Feb. 28, 2018
Stock authorized to purchase under stock repurchase program |  |  | $ 200,000,000
Repurchase of common stock, shares | 1,346,427 | 43,129,393 |
Repurchase of common stock, value | $ 31,100,000 | $ 524,400,000 |
Maximum [Member] |  |  |
Remaining value of shares authorized for purchase under the stock repurchase program | $ 200,000,000 | $ 200,000,000 |

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- Definition Number of shares that have been repurchased during the period and are being held in treasury. + 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 Reference 2: 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 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 505 -SubTopic 10 -Section 50 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=84159872&loc=d3e21463-112644 + Details
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