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		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Class of Stock [Line Items]
Weighted-average price for redemption of limited partnership units (in dollars per share)	$ 5.84	$ 3.05	$ 5.83	$ 3.92
Aggregate purchase price of Class A common stock			$ 107,783	$ 0
Limited Partnership
Class of Stock [Line Items]
Redeemed limited partnership units (in shares)	4,700	100	4,700	300
Aggregate redemption price of limited partnership units	$ 27,300	$ 300	$ 27,300	$ 1,300
FPUs
Class of Stock [Line Items]
Redeemed limited partnership units (in shares)	44	1	51	1
Aggregate redemption price of limited partnership units	$ 181	$ 4	$ 209	$ 4
Weighted-average price for redemption of founding/working partner units (in dollars per share)	$ 4.06	$ 3.07	$ 4.11	$ 3.07
Class A Common Stock
Class of Stock [Line Items]
Common stock, shares issued for redemption/cancellation of units (in shares)	13,800	700	15,400	2,100
Common stock, shares issued for exchange of units	16,800	1,300	25,900	1,800
Stock repurchased during period (in shares)	16,500		17,500
Aggregate purchase price of Class A common stock	$ 103,400		$ 107,800
Weighted-average price of Class A common stock (in dollars per share)	$ 6.25		$ 6.16