Secured Debt Agreements, Net - Credit Facilities (Detail) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Credit Facilities [Member]
Line of Credit Facility [Line Items]
Potential	$ 8,870,925	$ 9,210,325
Repurchase Borrowings Outstanding	8,065,675	8,870,897
Available	805,250	339,428
Collateral Assets	11,379,431	11,729,560
Deutsche Bank [Member]
Line of Credit Facility [Line Items]
Repurchase Borrowings Outstanding	850,700
Deutsche Bank [Member] \| Credit Facilities [Member]
Line of Credit Facility [Line Items]
Potential	1,861,121	1,839,698
Repurchase Borrowings Outstanding	1,861,121	1,839,698
Collateral Assets	2,353,629	2,325,047
Wells Fargo [Member]
Line of Credit Facility [Line Items]
Repurchase Borrowings Outstanding	171,500	314,000
Wells Fargo [Member] \| Credit Facilities [Member]
Line of Credit Facility [Line Items]
Potential	1,742,942	1,908,509
Repurchase Borrowings Outstanding	1,251,130	1,822,154
Available	491,812	86,355
Collateral Assets	2,285,101	2,514,513
JP Morgan [Member]
Line of Credit Facility [Line Items]
Repurchase Borrowings Outstanding		520,600
JP Morgan [Member] \| Credit Facilities [Member]
Line of Credit Facility [Line Items]
Potential	959,907	1,010,628
Repurchase Borrowings Outstanding	861,744	1,010,628
Available	98,163
Collateral Assets	1,221,674	1,266,259
Citibank [Member] \| Credit Facilities [Member]
Line of Credit Facility [Line Items]
Potential	1,006,592	852,470
Repurchase Borrowings Outstanding	922,804	663,917
Available	83,788	188,553
Collateral Assets	1,278,710	1,076,085
Barclays [Member] \| Credit Facilities [Member]
Line of Credit Facility [Line Items]
Potential	933,424	890,620
Repurchase Borrowings Outstanding	902,146	890,620
Available	31,278
Collateral Assets	1,166,780	1,113,275
Bank of America [Member] \| Credit Facilities [Member]
Line of Credit Facility [Line Items]
Potential	768,871	873,446
Repurchase Borrowings Outstanding	768,871	873,446
Collateral Assets	962,378	1,090,117
Morgan Stanley [Member] \| Credit Facilities [Member]
Line of Credit Facility [Line Items]
Potential	434,199	341,241
Repurchase Borrowings Outstanding	378,990	276,721
Available	55,209	64,520
Collateral Assets	576,614	457,496
Societe Generale [Member] \| Credit Facilities [Member]
Line of Credit Facility [Line Items]
Potential	321,182	321,182
Repurchase Borrowings Outstanding	321,182	321,182
Collateral Assets	419,034	404,048
Goldman Sachs [Member] \| Credit Facilities [Member]
Line of Credit Facility [Line Items]
Potential	292,753	230,140
Repurchase Borrowings Outstanding	247,753	230,140
Available	45,000
Collateral Assets	401,422	295,368
MetLife [Member] \| Credit Facilities [Member]
Line of Credit Facility [Line Items]
Potential	233,616	675,329
Repurchase Borrowings Outstanding	233,616	675,329
Collateral Assets	296,356	852,733
Goldman Sachs - Multi. JV [Member] \| Credit Facilities [Member]
Line of Credit Facility [Line Items]
Potential	219,316	170,060
Repurchase Borrowings Outstanding	219,316	170,060
Collateral Assets	293,877	212,983
Bank of America - Multi. JV [Member] \| Credit Facilities [Member]
Line of Credit Facility [Line Items]
Potential	97,002	97,002
Repurchase Borrowings Outstanding	97,002	97,002
Collateral Assets	$ 123,856	$ 121,636

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

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- 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.

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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
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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=6876686&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=6879938&loc=d3e572229-122910

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- 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.

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

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