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Dividends Declared Per Share (Detail) - $ / shares | 3 Months Ended | 6 Months Ended
--- | --- | ---
Jun. 30, 2018 | Jun. 30, 2017 | Jun. 30, 2018 | Jun. 30, 2017
Dividends Payable [Line Items] |  |  |  |
Dividend Amount | $ 0.365 | $ 0.360 | $ 0.730 | $ 0.720
Group One |  |  |  |
Dividends Payable [Line Items] |  |  |  |
Declaration Date |  |  | Jul. 25, 2018 |
Date Paid (Payable) |  |  | Aug. 29, 2018 |
Shareholder of Record Date |  |  | Aug. 15, 2018 |
Dividend Amount |  |  | $ 0.365 |
Group Two |  |  |  |
Dividends Payable [Line Items] |  |  |  |
Declaration Date |  |  | Apr. 25, 2018 |
Date Paid (Payable) |  |  | May 29, 2018 |
Shareholder of Record Date |  |  | May 15, 2018 |
Dividend Amount |  |  | $ 0.365 |
Group Three |  |  |  |
Dividends Payable [Line Items] |  |  |  |
Declaration Date |  |  | Jan. 30, 2018 |
Date Paid (Payable) |  |  | Feb. 28, 2018 |
Shareholder of Record Date |  |  | Feb. 14, 2018 |
Dividend Amount |  |  | $ 0.365 |
Group Four |  |  |  |
Dividends Payable [Line Items] |  |  |  |
Declaration Date |  |  | Oct. 25, 2017 |
Date Paid (Payable) |  |  | Nov. 29, 2017 |
Shareholder of Record Date |  |  | Nov. 15, 2017 |
Dividend Amount |  |  | $ 0.360 |
Group Five |  |  |  |
Dividends Payable [Line Items] |  |  |  |
Declaration Date |  |  | Jul. 26, 2017 |
Date Paid (Payable) |  |  | Aug. 29, 2017 |
Shareholder of Record Date |  |  | Aug. 15, 2017 |
Dividend Amount |  |  | $ 0.360 |
Group Six |  |  |  |
Dividends Payable [Line Items] |  |  |  |
Declaration Date |  |  | Apr. 26, 2017 |
Date Paid (Payable) |  |  | May 30, 2017 |
Shareholder of Record Date |  |  | May 16, 2017 |
Dividend Amount |  |  | $ 0.360 |
Group Seven |  |  |  |
Dividends Payable [Line Items] |  |  |  |
Declaration Date |  |  | Jan. 25, 2017 |
Date Paid (Payable) |  |  | Feb. 28, 2017 |
Shareholder of Record Date |  |  | Feb. 14, 2017 |
Dividend Amount |  |  | $ 0.360 |

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- Definition Aggregate dividends declared during the period for each share of common stock outstanding. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -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 Date the declared dividend will be paid, in CCYY-MM-DD format. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -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 + Details
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- Definition Date the dividend to be paid was declared, in CCYY-MM-DD format. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -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 + Details
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- Definition Date the holder must own the stock to be entitled to the dividend, in CCYY-MM-DD format. + References No definition available. + Details
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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
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