Investments in Commercial Mortgage Loans, Mezzanine Loans and Preferred Equity Interests - Additional Information (Detail) $ in Thousands		1 Months Ended		3 Months Ended			12 Months Ended
	May 08, 2019 USD ($)	May 31, 2019 USD ($)	Mar. 31, 2018 USD ($) Loan	Mar. 31, 2019 USD ($) Loan		Mar. 31, 2018 USD ($) Loan	Dec. 31, 2018 USD ($) Loan
Accounts Notes And Loans Receivable [Line Items]
Principal balance				$ 6,967
Unpaid Principal Balance			$ 90,260			$ 90,260
Benefit for loan losses				583		(8,032)
Average impaired loans unpaid balance				121,132		124,887
Interest income from impaired loans				0		$ 127
Recovery of amounts which previously charged off				$ 9,000
Proceeds from sale of loans held-for-sale			43,384
Loss on sale of loans			$ 930
Number of loans held for sale | Loan			9			9
Number of loans sold | Loan							6
Net loss on sale of loans							$ 3,280
Number of loans available for sale | Loan				3
Gain on loans available for sale				$ 303
Carrying amount of loans held for sale				5,131
Secured warehouse facility
Accounts Notes And Loans Receivable [Line Items]
Repayments of debt			$ 45,850
Interest paid			349
Subsequent Event
Accounts Notes And Loans Receivable [Line Items]
Settlement agreement, amount to be paid by related securitization trust	$ 9,000	$ 9,000
Commercial Portfolio Segment
Accounts Notes And Loans Receivable [Line Items]
Principal balance				$ 438,641	[1]		$ 503,071	[2]
Number of Loans | Loan				46	[1]		51	[2]
Unpaid Principal Balance				$ 438,542	[1]		$ 502,974	[2]
Commercial Portfolio Segment | One Commercial Mortgage Loan
Accounts Notes And Loans Receivable [Line Items]
Modification troubled debt restructuring, subsequently defaulted, number of loans | Loan				0		0
Modification troubled debt restructuring, number of loans | Loan				1		1
Unpaid principal balance constituted a TDR			$ 7,948	$ 29,478		$ 7,948
Percentage of interest payment rate			0.00%			0.00%
Commercial Portfolio Segment | Cash Flow Loans
Accounts Notes And Loans Receivable [Line Items]
Principal balance				$ 53,128			$ 54,621
Minimum | Commercial Portfolio Segment
Accounts Notes And Loans Receivable [Line Items]
Loan maturity				90 days			90 days
90 days or more | Commercial Portfolio Segment
Accounts Notes And Loans Receivable [Line Items]
Commercial real estate loans on non-accrual status				$ 81,967			$ 92,993
Weighted-average interest rate				6.80%			6.90%
Recognizing interest on the cash basis | Commercial Portfolio Segment
Accounts Notes And Loans Receivable [Line Items]
Weighted-average interest rate				11.40%			11.40%
Number of Loans | Loan				5			5
Unpaid Principal Balance				$ 25,703			$ 25,703
Loans Originated Prior to 2010
Accounts Notes And Loans Receivable [Line Items]
Benefit for loan losses				$ 583

[1] Includes $53,128 of cash flow loans, of which $7,148 are commercial mortgage loans, $21,114 are mezzanine loans and $24,866 are preferred equity interests. See Note 2: Summary of Significant Accounting Policies, (j) Revenue Recognition, for further discussion of our cash flow loans.

[2] Includes $54,621 of cash flow loans, of which $8,579 are commercial mortgage loans, $21,114 are mezzanine loans and $24,928 are preferred equity interests. See Note 2: Summary of Significant Accounting Policies, (j) Revenue Recognition, for further discussion of our cash flow loans.