XML 101 R85.htm IDEA: XBRL DOCUMENT v3.20.4
Stock Transactions and Unit Redemptions - Gross Unit Redemptions and Share Repurchases of Class A Common Stock (Parenthetical) (Detail) - USD ($)
 3 Months Ended 12 Months Ended
Sep. 30, 2020
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Class of Stock [Line Items]        
Weighted-average price for redemption of limited partnership units   $ 3.03 $ 5.92  
Repurchase of Class A common stock, shares Treasury Stock Shares Acquired 2,000 2,000    
Aggregate purchase price of Class A common stock   $ 6,000 $ 1,236,000 $ 10,439,000
Class A Common Stock [Member]        
Class of Stock [Line Items]        
Common stock, shares issued for redemption/cancellation of units   9,500,000 10,100,000  
Common stock, shares issued for exchange of units   3,700,000 4,400,000  
Repurchase of Class A common stock, shares Treasury Stock Shares Acquired   2,259 233,172 788,788
Aggregate purchase price of Class A common stock   $ 6,000 $ 1,200,000  
Weighted-average price of Class A common stock   $ 2.58 $ 5.30  
Limited Partnership [Member]        
Class of Stock [Line Items]        
Redeemed limited partnership units   1,800,000 1,400,000  
Aggregate redemption price of limited partnership units   $ 5,500,000 $ 8,000,000.0  
Other Ownership Interest [Member]        
Class of Stock [Line Items]        
Redeemed limited partnership units   700,000 56,900  
Aggregate redemption price of limited partnership units   $ 1,300,000 $ 320,600  
Weighted-average price for redemption of founding/working partner units   $ 1.79 $ 5.64