Condensed Consolidated Statements of Changes in Equity (Unaudited) (Parenthetical) - $ / shares	9 Months Ended
Sep. 30, 2018	Sep. 30, 2017
Class A Common Stock
Common stock dividends, per share	$ 0.42	$ 0.36

Aggregate dividends paid 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