Consolidated Statements of Changes in Equity (Parenthetical) - $ / shares  | 
12 Months Ended | ||
|---|---|---|---|
Dec. 31, 2018  | 
Dec. 31, 2017  | 
Dec. 31, 2016  | 
|
| Class A Common Stock | |||
| Common stock dividends, per share | $ 0.56 | $ 0.48 | $ 0.48 | 
| X | ||||||||||
- Definition Aggregate dividends paid during the period for each share of common stock outstanding. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef 
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| X | ||||||||||
- Details 
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