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Summary of Significant Accounting Policies - Earnings per Share (Details) - shares
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Restricted Stock and Stock Options      
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]      
Anti-dilutive restricted common stock units excluded from computation of earnings per share (in shares) 22,396 27,082 5,551