Other Assets and Liabilities - Summary of Unfunded Loan Commitment (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020	Jan. 01, 2020	Dec. 31, 2019
CECL reserve	$ 172,100	$ 112,694	$ 173,549		$ 0
(Decrease) Increase in CECL reserve	(1,449)	98,752
U.S. Loans [Member]
CECL reserve	44,534	64,861	42,995		0
(Decrease) Increase in CECL reserve	1,539	55,906
Non-U.S. Loans [Member]
CECL reserve	24,600	21,825	27,734		0
(Decrease) Increase in CECL reserve	(3,134)	18,194
Unfunded Loan Commitment [Member]
CECL reserve	11,021	22,536	10,031		0
(Decrease) Increase in CECL reserve	990	19,273
Unfunded Loan Commitment [Member] | U.S. Loans [Member]
CECL reserve	7,169	19,793	6,953		0
(Decrease) Increase in CECL reserve	216	16,992
Unfunded Loan Commitment [Member] | Non-U.S. Loans [Member]
CECL reserve	3,772	2,672	2,994		0
(Decrease) Increase in CECL reserve	778	2,219
Accounting Standards Update 2016-13 [Member]
CECL reserve				$ 13,942
Accounting Standards Update 2016-13 [Member] | U.S. Loans [Member]
CECL reserve				8,955
Accounting Standards Update 2016-13 [Member] | Non-U.S. Loans [Member]
CECL reserve				3,631
Accounting Standards Update 2016-13 [Member] | Unfunded Loan Commitment [Member]
CECL reserve	3,300			3,263
Accounting Standards Update 2016-13 [Member] | Unfunded Loan Commitment [Member] | U.S. Loans [Member]
CECL reserve				2,801
Accounting Standards Update 2016-13 [Member] | Unfunded Loan Commitment [Member] | Non-U.S. Loans [Member]
CECL reserve				453
Unique Loans [Member]
CECL reserve	33,305	26,008	33,159		0
(Decrease) Increase in CECL reserve	146	24,652
Unique Loans [Member] | Unfunded Loan Commitment [Member]
CECL reserve	80	71	84		0
(Decrease) Increase in CECL reserve	(4)	62
Unique Loans [Member] | Accounting Standards Update 2016-13 [Member]
CECL reserve				1,356
Unique Loans [Member] | Accounting Standards Update 2016-13 [Member] | Unfunded Loan Commitment [Member]
CECL reserve				9
Impaired Loans [Member]
CECL reserve	69,661	0	69,661		0
(Decrease) Increase in CECL reserve	0	0
Impaired Loans [Member] | Unfunded Loan Commitment [Member]
CECL reserve	0	0	$ 0		$ 0
(Decrease) Increase in CECL reserve	$ 0	$ 0
Impaired Loans [Member] | Accounting Standards Update 2016-13 [Member] | Unfunded Loan Commitment [Member]
CECL reserve				$ 0