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Consolidated Statements of Changes in Stockholders' Equity (Parenthetical) - $ / shares
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Statement of Stockholders' Equity [Abstract]      
Dividends declared on common stock (in dollars per share) $ 1.84 $ 1.84 $ 1.87