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Summary of Significant Accounting Policies - Common Stock and Convertible Stock Dilutive in Weighted average unearned PSUs outstanding (Detail) - $ / shares
shares in Thousands
3 Months Ended
Mar. 31, 2021
Mar. 31, 2020
Accounting Policies [Abstract]    
Weighted average PSUs 1,136 927
Weighted average grant date fair value per unit (in dollars per share) $ 9.33 $ 9.58