Net Income Per Share and Stockholders' Equity, Narrative (Details) - USD ($) shares in Millions, $ in Millions	9 Months Ended
Sep. 30, 2018	Sep. 30, 2017	Sep. 17, 2018
Earnings Per Share [Abstract]
Dividends paid	$ 28.5	$ 26.4
Stock Repurchase Program, Number of Shares Authorized to be Repurchased			100.0
Availability remaining to repurchase common shares pursuant to stock repurchase program	$ 178.3

Cash outflow in the form of capital distributions and dividends to common shareholders, preferred shareholders and noncontrolling interests.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 15
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=109223946&loc=d3e3291-108585

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