Summary of Significant Accounting Policies - Additional Information (Detail) $ in Thousands			3 Months Ended		12 Months Ended
		Aug. 30, 2019 USD ($)	Mar. 31, 2019 USD ($) Loan Property Instrument	Mar. 31, 2018 USD ($)	Dec. 31, 2018 USD ($) Loan	Jan. 01, 2019 USD ($) Property
Significant Accounting Policies [Line Items]
Decrease to cash flows from operating activities				$ (89,583)
Increase to cash flows from investing activities				89,583
Principal amount outstanding			$ 591,296		$ 642,559
Federal deposit insurance corporation, insurance limit per institution			250
Restricted cash			65,000	152,962	63,067
Accrued interest receivable			17,399		18,044
Earned asset management fees from consolidated securitizations, eliminated			59	162
Intangible assets, accumulated amortization			5,876		5,703
Intangible assets, amortization expenses			193	$ 427
Expected amortization expense of intangible assets, remainder of 2019			513
Expected amortization expense of intangible assets in 2020			434
Expected amortization expense of intangible assets in 2021			249
Expected amortization expense of intangible assets in 2022			145
Expected amortization expense of intangible assets in 2023			72
Expected amortization expense of intangible assets thereafter			$ 131
Number of derivative instruments outstanding | Instrument			0
Lease liability			$ 2,995
ROU asset			2,399
ASU Topic 842
Significant Accounting Policies [Line Items]
Lease liability						$ 3,008
ROU asset						$ 2,416
Number of real estate operating leases, recognition of lease liability and ROU asset | Property						1
In-place leases
Significant Accounting Policies [Line Items]
Intangible assets, gross carrying amount			$ 7,420		7,420
Multifamily real estate properties
Significant Accounting Policies [Line Items]
Number of real estate properties held | Property			0
Loans and Finance Receivables
Significant Accounting Policies [Line Items]
Accrued interest receivable			$ 15,503		15,870
Impairment of loans			$ 32,968		$ 33,030
Number of impaired loans | Loan			7		7
Minimum | Loans and Finance Receivables
Significant Accounting Policies [Line Items]
Stated interest rate			0.00%
Minimum | Building and Building Improvements
Significant Accounting Policies [Line Items]
Property, useful lives			30 years
Minimum | Furniture, fixtures, and equipment
Significant Accounting Policies [Line Items]
Property, useful lives			5 years
Maximum | Building and Building Improvements
Significant Accounting Policies [Line Items]
Property, useful lives			40 years
Maximum | Furniture, fixtures, and equipment
Significant Accounting Policies [Line Items]
Property, useful lives			10 years
Tenant escrows and borrowers' funds
Significant Accounting Policies [Line Items]
Restricted cash			$ 29,021		$ 33,300
Securitizations
Significant Accounting Policies [Line Items]
Restricted cash			35,979		29,767
Purchase Agreement | CF RFP Holdings LLC | Subsequent Event
Significant Accounting Policies [Line Items]
Purchase price		$ 174,424
Recourse Indebtedness
Significant Accounting Policies [Line Items]
Principal amount outstanding			$ 165,451		165,451
Recourse Indebtedness | 7.125% Senior Notes
Significant Accounting Policies [Line Items]
Stated interest rate			7.125%
Principal amount outstanding			$ 65,356		65,356
Contractual maturity date			Aug. 30, 2019
Recourse Indebtedness | 7.625% Senior Notes due 2024
Significant Accounting Policies [Line Items]
Stated interest rate			7.625%
Principal amount outstanding			$ 56,324		56,324
Recourse Indebtedness | Junior Subordinated Notes, at Amortized Cost
Significant Accounting Policies [Line Items]
Principal amount outstanding			25,100		25,100
Recourse Indebtedness | Junior Subordinated Notes, at Fair Value
Significant Accounting Policies [Line Items]
Principal amount outstanding	[1]		$ 18,671		$ 18,671

[1] Relates to liabilities which we elected to record at fair value under FASB ASC Topic 825.