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Consolidated Statements of Equity (Parenthetical) - shares
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Statement of Stockholders' Equity [Abstract]      
Issuance of shares of stock (in shares) 348,809 335,417 278,093
Shares of restricted common stock canceled (in shares) 52,676 33,720 47,418