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Condensed Consolidated Statements of Stockholders' Equity (Parenthetical) - $ / shares
9 Months Ended
Sep. 30, 2017
Sep. 30, 2016
Statement of Stockholders' Equity [Abstract]    
Cash dividends declared per common share (in dollars per share) $ 0.81 $ 0.52
Common stock issued per share for stock bonus (in USD per share) $ 44.26 $ 32.45