Condensed Consolidated Statements of Equity (Parenthetical) - $ / shares	3 Months Ended	9 Months Ended	12 Months Ended
Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Statement of Stockholders' Equity [Abstract]
Common dividends (in usd per share)	$ 0.205	$ 0.205	$ 0.205	$ 0.185	$ 0.615	$ 0.555	$ 0.74

Aggregate dividends declared during the period for each share of common stock outstanding.

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

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Namespace Prefix:	us-gaap_
Data Type:	num:perShareItemType
Balance Type:	na
Period Type:	duration