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Shareholders' Equity - Additional Information (Detail) - USD ($) $ in Thousands | Sep. 30, 2017 | Dec. 31, 2016
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Accelerated Share Repurchases [Line Items] |  |
Shares repurchased, number of shares received initially (in shares) | 9,319,545 | 8,003,197
Fair value of common stock repurchased | $ 315,072 | $ 257,683
Repurchase Agreements [Member] |  |
Accelerated Share Repurchases [Line Items] |  |
Shares repurchased, authorized amount | $ 100,000 |

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- Definition Number of common and preferred shares that were previously issued and that were repurchased by the issuing entity and held in treasury on the financial statement date. This stock has no voting rights and receives no dividends. + 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 210.5-02.29,30) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 505 -SubTopic 30 -Section 45 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6405813&loc=d3e23239-112655 + Details
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