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Capital Structure - Additional Information (Details)
 3 Months Ended
Mar. 31, 2019
class
vote
shares
Mar. 31, 2018
shares
Dec. 31, 2018
shares
Class of Stock [Line Items]      
Number of classes of common stock | class 4    
Non-voting common interest units outstanding (in shares) | shares 8,520,755   8,760,755
Number of non-voting common interest units forfeited or repurchased (in shares) | shares 240,000 3,540,312  
Class A common stock and Class C common stock      
Class of Stock [Line Items]      
Number of votes | vote 1    
Class B common stock and Class D common stock      
Class of Stock [Line Items]      
Number of votes | vote 10