Loan Participations Sold, Net - Summary of Statistics for Loan Participations Sold (Parenthetical) (Detail) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Participating Mortgage Loans [Line Items]
Deferred financing costs	$ 25,962	$ 21,725
Loan Participations Sold [Member]
Participating Mortgage Loans [Line Items]
Deferred financing costs		$ 110,000

Amount, after accumulated amortization, of debt issuance costs. Includes, but is not limited to, legal, accounting, underwriting, printing, and registration costs.

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 210.5-02.17)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=114775744&loc=d3e28555-108399

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant