Other Expenses - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2020	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
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) net income (loss) attributable to our legacy portfolio, (v) certain non-cash items, and (vi) incentive management fees.
Management fees		$ 77,916	$ 78,435	$ 74,834
Manager [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Management fees		60,400	55,300	47,000
Total incentive compensation payments		17,500	23,200	27,900
Accrued management and incentive fees payable		19,200	20,200
Management fees paid to Manager		$ 78,900	$ 76,900	$ 70,500
Manager [Member] | Class A Common Stock [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock Issued During Period, Shares, Issued for Services	840,696	840,696
Management fees paid to Manager	$ 19,300