Summary of Total Recourse and Non-Recourse Indebtedness (Parenthetical) (Detail) - Non Recourse Indebtedness - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
CMBS securitizations
Debt Instrument [Line Items]
Underlying collateral	$ 355,699	$ 409,218
CDO notes payable, at amortized cost
Debt Instrument [Line Items]
Underlying collateral	150,845	170,124
Consolidation Eliminations
Debt Instrument [Line Items]
Underlying collateral	78,979	$ 94,191
Consolidation Eliminations \| CMBS securitizations
Debt Instrument [Line Items]
Underlying collateral	$ 8,892

Carrying amount as of the balance sheet date of loans that have been pledged as collateral for borrowings. If the secured party has the right by contract or custom to sell or re-pledge the collateral, then the debtor reclassifies that asset and report that asset in its statement of financial position separately from other assets not so encumbered.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 30
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=66007379&loc=d3e113888-111728

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=84173941&loc=d3e5086-111524

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