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Income Per Share Information - Narrative (Details) - shares
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Contingently Issuable Shares      
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]      
Shares excluded in computation of diluted income per share (in shares) 567,589 374,555 259,274