Transactions with Related Parties - Additional Information (Detail) £ in Millions	3 Months Ended		12 Months Ended
	Mar. 31, 2020 USD ($) shares	Mar. 31, 2019 USD ($)	Dec. 31, 2019 USD ($) shares	Mar. 31, 2019 GBP (£)
Related Party Transaction [Line Items]
Non-cash expenses	$ 8,678,000	$ 7,768,000
Manager [Member]
Related Party Transaction [Line Items]
Management Agreement renewal term, description	the current term of which expires on December 19, 2020, and will be automatically renewed for a one-year term upon such date and each anniversary thereafter unless earlier terminated.
Restricted Class A Common Stock [Member]
Related Party Transaction [Line Items]
Management Agreement renewal term, period	1 year
Shares held | shares	1,887,067		1,698,582
Senior Term Facility [Member]
Related Party Transaction [Line Items]
Minority participation in senior term facility				49.00%
Manager [Member]
Related Party Transaction [Line Items]
Management Agreement expiration date	Dec. 19, 2020
Accrued management and incentive fees payable	$ 19,300,000		$ 20,200,000
Management fees paid to Manager	20,200,000		18,600,000
Expenses reimbursed to Manager	$ 218,000		$ 188,000
Manager [Member] | Class A Common Stock [Member] | Restricted Class A Common Stock [Member]
Related Party Transaction [Line Items]
Shares held | shares	936,653
Non-cash expenses	$ 4,300,000
Manager [Member] | Class A Common Stock [Member] | Restricted Class A Common Stock [Member] | Manager [Member]
Related Party Transaction [Line Items]
Non-cash expenses	32,100,000	3,800,000
Affiliates of Manager [Member] | Third-Party Service Provider [Member]
Related Party Transaction [Line Items]
Administrative services expenses incurred	133,000	$ 86,000
Blackstone-Advised Investment Vehicles, or the Funds [Member] | Senior Term Facility [Member]
Related Party Transaction [Line Items]
Loan face amount	421,500,000			£ 490.0
Senior term facility	$ 140,000,000.0			£ 240.1
Minority participation in senior term facility	33.00%