Summary of Significant Accounting Policies - Schedule of Impact of this Adoption (Detail) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current expected credit loss reserve	$ 112,694	$ 112,694
Impact of ASU 2016-13 Adoption [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current expected credit loss reserve	17,650
CECL reserve on unfunded loan commitments [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current expected credit loss reserve	22,536		$ 0
CECL reserve on unfunded loan commitments [Member] | Impact of ASU 2016-13 Adoption [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current expected credit loss reserve	3,263	3,263
US Loans [Member] | Impact of ASU 2016-13 Adoption [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current expected credit loss reserve	8,955
US Loans [Member] | CECL reserve on unfunded loan commitments [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current expected credit loss reserve	19,793		0
US Loans [Member] | CECL reserve on unfunded loan commitments [Member] | Impact of ASU 2016-13 Adoption [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current expected credit loss reserve		2,801
Non-US Loans [Member] | Impact of ASU 2016-13 Adoption [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current expected credit loss reserve	3,631
Non-US Loans [Member] | CECL reserve on unfunded loan commitments [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current expected credit loss reserve	2,672		0
Non-US Loans [Member] | CECL reserve on unfunded loan commitments [Member] | Impact of ASU 2016-13 Adoption [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current expected credit loss reserve		453
Unique Loans [Member] | Impact of ASU 2016-13 Adoption [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current expected credit loss reserve	1,356	0
Unique Loans [Member] | CECL reserve on unfunded loan commitments [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current expected credit loss reserve	71		$ 0
Unique Loans [Member] | CECL reserve on unfunded loan commitments [Member] | Impact of ASU 2016-13 Adoption [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current expected credit loss reserve		$ 9
CECL reserve on loans [Member] | Impact of ASU 2016-13 Adoption [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current expected credit loss reserve	13,942
CECL reserve on held-to-maturity debt securities [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current expected credit loss reserve	(5,122)
CECL reserve on held-to-maturity debt securities [Member] | Impact of ASU 2016-13 Adoption [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current expected credit loss reserve	$ 445