Variable Interest Entities - Summary of Assets and Liabilities of Variable Interest Entities (Detail) - USD ($) $ in Thousands		Mar. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Variable Interest Entity [Line Items]
Residential mortgage loans held-for-investment through consolidated securitization trusts, net for allowance of credit losses of $167 at March 31, 2020 and $175 at December 31, 2019	[1]	$ 416,571	$ 458,348
Accrued interest receivable		12,279	16,398
Total Assets		3,551,011	4,938,631
Accrued interest payable		11,942	16,757
Asset-backed securities issued by securitization trusts	[1]	407,243	448,987
Total Liabilities		3,166,962	4,366,679
Residential Mortgage Backed Securities
Variable Interest Entity [Line Items]
Residential mortgage loans held-for-investment through consolidated securitization trusts, net for allowance of credit losses of $167 at March 31, 2020 and $175 at December 31, 2019		141,645	152,922	$ 11,660
Variable Interest Entities Primary Beneficiary
Variable Interest Entity [Line Items]
Accrued interest receivable		1,300	1,500
Total Assets		418,000	460,000
Accrued interest payable		1,300	1,400
Asset-backed securities issued by securitization trusts		407,200	449,000
Total Liabilities		409,000	450,000
Variable Interest Entities Primary Beneficiary | Residential Mortgage Backed Securities
Variable Interest Entity [Line Items]
Residential mortgage loans held-for-investment through consolidated securitization trusts, net for allowance of credit losses of $167 at March 31, 2020 and $175 at December 31, 2019		416,571	458,348	$ 549,016
Accrued interest receivable		1,337	1,495
Total Assets		417,908	459,843
Accrued interest payable		1,291	1,448
Asset-backed securities issued by securitization trusts		407,243	448,987
Total Liabilities		$ 408,534	$ 450,435

[1] The consolidated balance sheets include assets of consolidated variable interest entities, or VIEs, that can only be used to settle obligations and liabilities of the VIEs for which creditors do not have recourse to the Company. At March 31, 2020 and December 31, 2019, total assets of the consolidated VIEs were $418 million and $460 million (including accrued interest receivable of $1.3 million and $1.5 million), respectively (which is recorded above in the line item entitled “Interest receivable”), and total liabilities were $409 million and $450 million (including accrued interest payable of $1.3 million and $1.4 million), respectively (which is recorded in the line item above entitled “Accrued interest payable”). Please refer to Note 5, “Variable Interest Entities,” for further discussion.See accompanying notes to unaudited consolidated financial statements.