Other Expenses - Schedule of General and Administrative Expenses (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Professional services	$ 1,969	$ 1,715	$ 5,831	$ 5,130
Operating and other costs	792	878	2,093	3,212
Subtotal	2,761	2,593	7,924	8,342
Non-cash compensation expenses
Restricted class A common stock earned	7,907	8,524	23,762	25,603
Director stock-based compensation	173	125	422	375
Subtotal	8,080	8,649	24,184	25,978
Total general and administrative expenses	$ 10,841	$ 11,242	$ 32,108	$ 34,320