Loan Participations Sold, Net - Summary of Statistics for Loan Participations Sold (Detail)	3 Months Ended	12 Months Ended
Mar. 31, 2019 USD ($) SecurityLoan	Dec. 31, 2018 USD ($) SecurityLoan
Participating Mortgage Loans [Line Items]
Count \| SecurityLoan	1	1
Principal Balance	$ 140,504,000	$ 123,745,000
Guarantee	0	0
Book Value, Total Loan	$ 14,508,735,000	$ 14,191,200,000
Weighted Average Term	2022-02	2022-02
Book Value	$ 107,237,000	$ 94,418,000
Senior Participation [Member]
Participating Mortgage Loans [Line Items]
Count \| SecurityLoan	1	1
Principal Balance	$ 107,330,000	$ 94,528,000
Guarantee	$ 0	$ 0
Weighted Average Term	2022-02	2022-02
Book Value	$ 107,237,000	$ 94,418,000
Loan Participations Sold [Member]
Participating Mortgage Loans [Line Items]
Book Value, Total Loan	$ 139,504,000	$ 122,669,000
LIBOR [Member]
Participating Mortgage Loans [Line Items]
Weighted Average Yield/Cost	5.96%	5.92%
LIBOR [Member] \| Senior Participation [Member]
Participating Mortgage Loans [Line Items]
Weighted Average Yield/Cost	4.06%	4.07%

Number Of Loan Participations Sold

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- Definition

Participating Mortgage Loans Participation Liabilities Principal Amount

+ References

No definition available.

+ Details

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- Definition

Participations sold loan guarantee value.

+ References

No definition available.

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- Definition

Participations sold loan weighted average term.

+ References

No definition available.

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- Definition

Participations Sold Loan Yield

+ References

No definition available.

+ Details

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- Definition

Amount before allowance and after deduction of deferred interest and fees, unamortized costs and premiums and discounts from face amounts, of loans and leases held in portfolio, including but not limited to, commercial and consumer loans. Excludes loans and leases covered under loss sharing agreements.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=82891408&loc=d3e4428-111522

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=84173941&loc=d3e5074-111524

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

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- Definition

The aggregate amount of the participation liability at the end of the accounting period.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 30
-Section 50
-Paragraph 1
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=99377297&loc=d3e10013-112621

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