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Stockholders' Equity - Narrative (Details)
shares in Thousands
Sep. 30, 2021
vote
shares
Dec. 31, 2020
shares
Class A Common Stock    
Class of Stock [Line Items]    
Common stock shares outstanding (in shares) | shares 19,786 18,304
Vote per share (in votes) | vote 1  
Class B Common Stock    
Class of Stock [Line Items]    
Common stock shares outstanding (in shares) | shares 17,239 18,447
Vote per share (in votes) | vote 1