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Consolidated Statements of Shareholder's Equity (Parenthetical) - $ / shares
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Statement of Stockholders' Equity [Abstract]      
Dividends declared, per common share (in usd per share) $ 0.52 $ 0.49 $ 0.48