Stock Transactions and Unit Redemptions - Gross Unit Redemptions and Share Repurchases of Class A Common Stock Table Footnote (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Class of Stock [Line Items]
Weighted-average price for redemption of limited partnership units (in dollars per share)	$ 4.47	$ 2.81	$ 5.83
Aggregate purchase price of Class A common stock			$ 227,052	$ 6
Limited Partnership
Class of Stock [Line Items]
Redeemed limited partnership units (in shares)	16	1,500	4,700	1,800
Aggregate redemption price of limited partnership units	$ 71	$ 4,100	$ 27,400	$ 5,400
Weighted-average price for redemption of founding/working partner units (in dollars per share)				$ 3.02
FPUs
Class of Stock [Line Items]
Redeemed limited partnership units (in shares)	57	27	100	28
Aggregate redemption price of limited partnership units	$ 302	$ 73	$ 500	$ 77
Weighted-average price for redemption of founding/working partner units (in dollars per share)	$ 5.33	$ 2.74	$ 4.75	$ 2.75
Class A Common Stock
Class of Stock [Line Items]
Common stock, shares issued for redemption/cancellation of units (in shares)	5,800	500	21,200	2,600
Common stock, shares issued for exchange of units	2,900	1,300	28,800	3,100
Stock repurchased during period (in shares)	24,400	2	41,900	2
Aggregate purchase price of Class A common stock	$ 126,800	$ 6	$ 234,600	$ 6
Weighted-average price of Class A common stock (in dollars per share)	$ 5.19	$ 2.58	$ 5.59	$ 2.58