Loans Held for Investment by Credit Risk Category (Detail) - USD ($) $ in Thousands	Jun. 30, 2019		Dec. 31, 2018		Mar. 31, 2018
Financing Receivable Recorded Investment [Line Items]
Unpaid Principal Balance					$ 90,260
Commercial Portfolio Segment
Financing Receivable Recorded Investment [Line Items]
Unpaid Principal Balance	$ 381,607	[1]	$ 502,974	[2]
Commercial Portfolio Segment | Commercial Mortgage Loans
Financing Receivable Recorded Investment [Line Items]
Unpaid Principal Balance	332,040		453,283
Commercial Portfolio Segment | Mezzanine Loans
Financing Receivable Recorded Investment [Line Items]
Unpaid Principal Balance	21,114		21,114
Commercial Portfolio Segment | Preferred Equity Interests
Financing Receivable Recorded Investment [Line Items]
Unpaid Principal Balance	28,453		28,577
Commercial Portfolio Segment | Satisfactory
Financing Receivable Recorded Investment [Line Items]
Unpaid Principal Balance	221,305		319,167
Commercial Portfolio Segment | Satisfactory | Commercial Mortgage Loans
Financing Receivable Recorded Investment [Line Items]
Unpaid Principal Balance	216,242		314,104
Commercial Portfolio Segment | Satisfactory | Preferred Equity Interests
Financing Receivable Recorded Investment [Line Items]
Unpaid Principal Balance	5,063		5,063
Commercial Portfolio Segment | Watchlist
Financing Receivable Recorded Investment [Line Items]
Unpaid Principal Balance	160,302	[3]	183,807	[4]
Commercial Portfolio Segment | Watchlist | Commercial Mortgage Loans
Financing Receivable Recorded Investment [Line Items]
Unpaid Principal Balance	115,798	[3]	139,179	[4]
Commercial Portfolio Segment | Watchlist | Mezzanine Loans
Financing Receivable Recorded Investment [Line Items]
Unpaid Principal Balance	21,114	[3]	21,114	[4]
Commercial Portfolio Segment | Watchlist | Preferred Equity Interests
Financing Receivable Recorded Investment [Line Items]
Unpaid Principal Balance	$ 23,390	[3]	$ 23,514	[4]

[1] Includes $51,017 of cash flow loans, of which $5,099 are commercial mortgage loans, $21,114 are mezzanine loans and $24,804 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.

[3] Includes $106,052 of loans that are considered to be impaired and $54,250 of loans that are not considered to be impaired.

[4] Includes $126,645 of loans that are considered to be impaired and $57,162 of loans that are not considered impaired.