Schedule IV - Mortgage Loans on Real Estate (Parenthetical) (Detail) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Tax basis of mortgage loans	$ 15,200,000
Net book value of restructured loan	16,399,166	$ 16,164,801	$ 14,191,200
Increase in CECL reserve	(173,549)
Reduction in Loan Spread and Extension in Maturity Date [Member]
Financing receivable troubled debt restructuring premodification recorded investment	338,700
Impaired Loans [Member]
Increase in CECL reserve	69,700
COVID-19 pandemic [Member]
Net book value of restructured loan	$ 173,500

Tax basis of mortgage loans.

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- Definition

Amount of increase (decrease) of allowance reserve for credit loss.

+ References

No definition available.

+ Details

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- Definition

Amount, before troubled debt restructuring, of financing receivable to be modified.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 33
-URI http://asc.fasb.org/extlink&oid=121611835&loc=SL6953676-111524

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- Definition

The balance represents the amount of loans that are secured by real estate mortgages, offset by the reserve to cover probable credit losses on the loan portfolio.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03.1(c))
-URI http://asc.fasb.org/extlink&oid=120400017&loc=d3e572229-122910

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