Secured Debt, Net - Schedule of All in Cost of Secured Credit Facilities (Parenthetical) (Detail) - Credit Facilities [Member]	9 Months Ended	12 Months Ended
	Sep. 30, 2021	Dec. 31, 2020
USD LIBOR Rate [Member]
Schedule Of All In Cost Of Secured Credit Facilities [Line Items]
Basis spread on debt obligation, in percent	1.50%	1.50%
GBP LIBOR [Member] | Maximum [Member]
Schedule Of All In Cost Of Secured Credit Facilities [Line Items]
Basis spread on debt obligation, in percent	1.75%	1.75%
GBP LIBOR [Member] | Minimum [Member]
Schedule Of All In Cost Of Secured Credit Facilities [Line Items]
Basis spread on debt obligation, in percent	1.51%	1.51%
Sterling Overnight Interbank Average Rate [Member] | Maximum [Member]
Schedule Of All In Cost Of Secured Credit Facilities [Line Items]
Basis spread on debt obligation, in percent	2.00%	2.00%
Sterling Overnight Interbank Average Rate [Member] | Minimum [Member]
Schedule Of All In Cost Of Secured Credit Facilities [Line Items]
Basis spread on debt obligation, in percent	1.76%	1.76%
Sek [Member]
Schedule Of All In Cost Of Secured Credit Facilities [Line Items]
Basis spread on debt obligation, in percent	2.01%	2.01%