Other Expenses - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Management fee - percent of outstanding equity balance			1.50%
Incentive fee computation-percent of the product per agreement			20.00%
Incentive fee computation-percent of outstanding Equity per annum			7.00%
Management fees description			our Manager earns a base management fee in an amount equal to 1.50% per annum multiplied by our outstanding equity balance, as defined in the Management Agreement. In addition, our Manager is entitled to an incentive fee in an amount equal to the product of (i) 20% and (ii) the excess of (a) our Core Earnings (as defined in our Management Agreement) for the previous 12-month period over (b) an amount equal to 7.00% per annum multiplied by our outstanding Equity, provided that our Core Earnings over the prior three-year period is greater than zero. Core Earnings, as defined in our Management Agreement, is generally equal to our GAAP net income (loss), including realized gains and losses not otherwise recognized in current period GAAP net income (loss), and excluding (i) non-cash equity compensation expense, (ii) depreciation and amortization, (iii) unrealized gains (losses), (iv) certain non-cash items, and (v) incentive management fees.
Management fees	$ 19,342	$ 18,985	$ 60,094	$ 58,758
Manager [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Management fees	15,800	15,600	46,900	44,800
Total incentive compensation payments	3,600	$ 3,400	13,200	13,900
Accrued management and incentive fees payable	$ 19,300		19,300		$ 19,200
Payment for management and incentive fees			$ 59,900	40,700
Manager [Member] | Class A Common Stock [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock Issued During Period, Value, Issued for Services				$ 19,300
Stock Issued During Period, Shares, Issued for Services				840,696