v3.8.0.1

Subsequent Events (Narrative) (Details) - $ / shares |  | 12 Months Ended
--- | --- | ---
Feb. 07, 2018 | Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
Subsequent Event [Line Items] |  |  |  |
Dividends declared per share of Common Stock (in dollars per share) |  | $ 3.00 | $ 2.80 | $ 2.44
Subsequent Event |  |  |  |
Subsequent Event [Line Items] |  |  |  |
Dividends declared per share of Common Stock (in dollars per share) | $ 0.90 |  |  |

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- Definition Aggregate dividends declared 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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Namespace Prefix: | us-gaap_
Data Type: | num:perShareItemType
Balance Type: | na
Period Type: | duration

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- Definition Detail information of subsequent event by type. User is expected to use existing line items from elsewhere in the taxonomy as the primary line items for this disclosure, which is further associated with dimension and member elements pertaining to a subsequent event. + References No definition available. + Details
Name: | us-gaap_SubsequentEventLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Details
Name: | us-gaap_SubsequentEventTypeAxis=us-gaap_SubsequentEventMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |