Other Expenses - Schedule of General and Administrative Expenses (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Professional services	$ 2,043	$ 1,752	$ 3,861	$ 3,414
Operating and other costs	606	882	1,301	2,335
Subtotal	2,649	2,634	5,162	5,749
Non-cash compensation expenses
Restricted class A common stock earned	7,895	8,527	15,855	17,079
Director stock-based compensation	125	125	250	250
Subtotal	8,020	8,652	16,105	17,329
Total general and administrative expenses	$ 10,669	$ 11,286	$ 21,267	$ 23,078