Other Assets and Liabilities - Summary of Unfunded Loan Commitment (Detail) - USD ($) $ in Thousands	3 Months Ended
	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2020	Jan. 01, 2020	Dec. 31, 2019
CECL reserve	$ 130,388	$ 128,945	$ 172,100	$ 177,026	$ 178,050	$ 112,694	$ 173,549		$ 0
(Decrease) Increase in CECL reserve	98,752	(43,155)	(1,449)	(1,024)	65,356	1,443
U.S. Loans [Member]
CECL reserve	20,926	17,673	44,534	50,642	61,404	64,861	42,995
(Decrease) Increase in CECL reserve	55,906	(26,861)	1,539	(10,762)	(3,457)	3,253
Non-U.S. Loans [Member]
CECL reserve	8,546	8,829	24,600	26,780	19,745	21,825	27,734
(Decrease) Increase in CECL reserve	18,194	(15,771)	(3,134)	7,035	(2,080)	(283)
Unfunded Loan Commitment [Member]
CECL reserve	5,203	4,037	11,021	12,057	15,002	22,536	10,031		0
(Decrease) Increase in CECL reserve	1,166	(6,984)	990	(2,945)	(7,534)	19,273
Unfunded Loan Commitment [Member] | U.S. Loans [Member]
CECL reserve	3,420	2,854	7,169	9,179	12,836	19,793	6,953		0
(Decrease) Increase in CECL reserve	566	(4,315)	216	(3,657)	(6,957)	16,992
Unfunded Loan Commitment [Member] | Non-U.S. Loans [Member]
CECL reserve	1,783	1,140	3,772	2,810	2,078	2,672	2,994		0
(Decrease) Increase in CECL reserve	643	(2,632)	778	732	(594)	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	31,255	32,782	33,305	29,943	27,240	26,008	33,159		0
(Decrease) Increase in CECL reserve	24,652	(523)	146	2,703	1,232	(1,527)
Unique Loans [Member] | Unfunded Loan Commitment [Member]
CECL reserve	0	43	80	68	88	71	84		0
(Decrease) Increase in CECL reserve	(43)	(37)	(4)	(20)	17	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	69,661	69,661	69,661	69,661	0	69,661		0
(Decrease) Increase in CECL reserve	0	0	0	0	69,661	0
Impaired Loans [Member] | Unfunded Loan Commitment [Member]
CECL reserve	0	0	0	0	0	0	$ 0		$ 0
(Decrease) Increase in CECL reserve	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0
Impaired Loans [Member] | Accounting Standards Update 2016-13 [Member]
CECL reserve								0
Impaired Loans [Member] | Accounting Standards Update 2016-13 [Member] | Unfunded Loan Commitment [Member]
CECL reserve								$ 0