Equity Cash Dividends on Common Stock (Details) - USD ($) $ / shares in Units, $ in Millions		3 Months Ended
Jan. 23, 2018	Mar. 31, 2018	Mar. 31, 2017
Class of Stock [Line Items]
Cash dividends declared per common share	$ 0.36	$ 0.36	$ 0.33
Aggregate amount of dividend declared	$ 36.9	$ 36.9	$ 35.0

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.

No definition available.

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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

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- Definition

Amount of paid and unpaid common stock dividends declared with the form of settlement in cash.

+ References

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