Variable Interest Entities - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended
Sep. 30, 2018	Mar. 31, 2021
Variable Interest Entity [Line Items]
Subordinate risk retention interest notional amount	$ 99.0
Loans Receivable [Member]
Variable Interest Entity [Line Items]
Loan contributed to securitization	517.5
2018 Single Asset Securitization [Member]
Variable Interest Entity [Line Items]
Single asset securitization principal amount	$ 1,000.0
Maximum exposure to loss		$ 76.7

The reporting entity's maximum amount of exposure to loss as a result of its involvement with the Variable Interest Entity (VIE).

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 810
-SubTopic 10
-Section 50
-Paragraph 6
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=121559654&loc=d3e5747-111685

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 810
-SubTopic 10
-Section 50
-Paragraph 4
-Subparagraph b
-URI http://asc.fasb.org/extlink&oid=121559654&loc=d3e5728-111685

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