Secured Debt Agreements, Net - Credit Facilities (Detail) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Line of Credit Facility [Line Items]
Potential	$ 8,979,644	$ 8,726,028
Repurchase Borrowings Outstanding	8,142,728	7,896,863
Available	836,916	829,165
Collateral Assets	12,322,071	12,040,907
Credit Facilities [Member]
Line of Credit Facility [Line Items]
Potential	8,979,644
Repurchase Borrowings Outstanding	8,142,728	7,900,000
Barclays [Member] \| Credit Facilities [Member]
Line of Credit Facility [Line Items]
Potential	1,679,748	1,443,251
Repurchase Borrowings Outstanding	1,523,419	1,249,415
Available	156,329	193,836
Collateral Assets	2,156,809	1,862,987
Deutsche Bank [Member]
Line of Credit Facility [Line Items]
Repurchase Borrowings Outstanding	845,400
Deutsche Bank [Member] \| Credit Facilities [Member]
Line of Credit Facility [Line Items]
Potential	1,604,238	1,892,211
Repurchase Borrowings Outstanding	1,498,113	1,847,211
Available	106,125	45,000
Collateral Assets	2,494,076	2,869,889
Wells Fargo [Member]
Line of Credit Facility [Line Items]
Repurchase Borrowings Outstanding	136,800	182,500
Wells Fargo [Member] \| Credit Facilities [Member]
Line of Credit Facility [Line Items]
Potential	1,424,351	1,241,357
Repurchase Borrowings Outstanding	1,190,799	956,780
Available	233,552	284,577
Collateral Assets	1,885,248	1,663,661
Citibank [Member] \| Credit Facilities [Member]
Line of Credit Facility [Line Items]
Potential	981,763	927,531
Repurchase Borrowings Outstanding	815,675	779,139
Available	166,088	148,392
Collateral Assets	1,277,834	1,212,521
Goldman Sachs [Member] \| Credit Facilities [Member]
Line of Credit Facility [Line Items]
Potential	598,435	615,411
Repurchase Borrowings Outstanding	598,435	615,411
Collateral Assets	806,252	828,965
Bank of America [Member] \| Credit Facilities [Member]
Line of Credit Facility [Line Items]
Potential	468,061	473,678
Repurchase Borrowings Outstanding	468,061	473,678
Collateral Assets	658,692	667,830
Morgan Stanley [Member] \| Credit Facilities [Member]
Line of Credit Facility [Line Items]
Potential	531,877	528,846
Repurchase Borrowings Outstanding	404,877	401,846
Available	127,000	127,000
Collateral Assets	854,924	849,426
MetLife [Member] \| Credit Facilities [Member]
Line of Credit Facility [Line Items]
Potential	284,900	276,605
Repurchase Borrowings Outstanding	284,900	276,605
Collateral Assets	356,125	349,612
JP Morgan [Member] \| Credit Facilities [Member]
Line of Credit Facility [Line Items]
Potential	453,589	449,449
Repurchase Borrowings Outstanding	409,236	422,096
Available	44,353	27,353
Collateral Assets	610,048	605,144
US Bank—Multi. JV [Member] \| Credit Facilities [Member]
Line of Credit Facility [Line Items]
Potential	234,864	184,802
Repurchase Borrowings Outstanding	231,395	181,795
Available	3,469	3,007
Collateral Assets	293,580	231,003
Goldman Sachs—Multi. JV [Member] \| Credit Facilities [Member]
Line of Credit Facility [Line Items]
Potential	217,890	167,964
Repurchase Borrowings Outstanding	217,890	167,964
Collateral Assets	294,101	231,840
Société Générale [Member] \| Credit Facilities [Member]
Line of Credit Facility [Line Items]
Potential	240,338	237,822
Repurchase Borrowings Outstanding	240,338	237,822
Collateral Assets	309,894	308,700
Santander [Member] \| Credit Facilities [Member]
Line of Credit Facility [Line Items]
Potential	259,590	269,501
Repurchase Borrowings Outstanding	259,590	269,501
Collateral Assets	$ 324,488	337,329
Bank of America—Multi. JV [Member] \| Credit Facilities [Member]
Line of Credit Facility [Line Items]
Potential		17,600
Repurchase Borrowings Outstanding		17,600
Collateral Assets		$ 22,000

Amount of assets pledged to secure a debt instrument.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 470
-Section 50
-Paragraph 3
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=75038535&loc=d3e64711-112823

+ Details

Name:	us-gaap_DebtInstrumentCollateralAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

The carrying value as of the balance sheet date of the current and noncurrent portions of long-term obligations drawn from a line of credit, which is a bank's commitment to make loans up to a specific amount. Examples of items that might be included in the application of this element may consist of letters of credit, standby letters of credit, and revolving credit arrangements, under which borrowings can be made up to a maximum amount as of any point in time conditional on satisfaction of specified terms before, as of and after the date of drawdowns on the line. Includes short-term obligations that would normally be classified as current liabilities but for which (a) postbalance sheet date issuance of a long term obligation to refinance the short term obligation on a long term basis, or (b) the enterprise has entered into a financing agreement that clearly permits the enterprise to refinance the short-term obligation on a long term basis and the following conditions are met (1) the agreement does not expire within 1 year and is not cancelable by the lender except for violation of an objectively determinable provision, (2) no violation exists at the BS date, and (3) the lender has entered into the financing agreement is expected to be financially capable of honoring the agreement.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(22))
-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(16))
-URI http://asc.fasb.org/extlink&oid=120398452&loc=d3e534808-122878

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03(16))
-URI http://asc.fasb.org/extlink&oid=120400017&loc=d3e572229-122910

+ Details

Name:	us-gaap_LineOfCredit
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of current borrowing capacity under the credit facility considering any current restrictions on the amount that could be borrowed (for example, borrowings may be limited by the amount of current assets), but without considering any amounts currently outstanding under the facility.

+ References

+ Details

Name:	us-gaap_LineOfCreditFacilityCurrentBorrowingCapacity
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

Name:	us-gaap_LineOfCreditFacilityLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of borrowing capacity currently available under the credit facility (current borrowing capacity less the amount of borrowings outstanding).

+ References

+ Details

Name:	us-gaap_LineOfCreditFacilityRemainingBorrowingCapacity
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant