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Consolidated Statements of Equity (Parenthetical) - $ / shares
3 Months Ended 12 Months Ended
Dec. 31, 2017
Sep. 30, 2017
Jun. 30, 2017
Mar. 31, 2017
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Statement of Stockholders' Equity [Abstract]              
Dividends per share (in dollars per share) $ 0.52 $ 0.52 $ 0.52 $ 0.52 $ 2.08 $ 1.98 $ 1.74