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Summary of Significant Accounting Policies - Earnings per Share (Details) - shares
shares in Thousands
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Accounting Policies [Abstract]      
Common stock equivalents (in shares) 412 586 513
Antidilutive common stock equivalents (in shares) 249 1 0