Fair Value of Financial Instruments - Additional Information (Detail) $ in Thousands		3 Months Ended	6 Months Ended
		Jun. 30, 2018 USD ($) Loan Property	Jun. 30, 2018 USD ($) Loan Property	Dec. 31, 2017 USD ($)
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets Fair Value Disclosure				$ 11
Number of Loans | Loan		9	9
Non-Recurring Fair Value Measurements | Commercial Real Estate
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets Fair Value Disclosure		$ 111,867	$ 111,867
Number of Loans | Loan			11
Significant Other Observable Inputs (Level 2)
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets Fair Value Disclosure	[1]			$ 11
Significant Other Observable Inputs (Level 2) | Non-Recurring Fair Value Measurements | Purchase and Sale Agreement
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets Fair Value Disclosure		$ 28,440	$ 28,440
Number real estate asset | Property		1	1
Significant Other Observable Inputs (Level 2) | Non-Recurring Fair Value Measurements | Letters of Intent
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets Fair Value Disclosure		$ 55,650	$ 55,650
Number real estate asset | Property		3	3
Junior Subordinated Notes, at Fair Value
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Debt Instrument, Valuation Technique [Extensible List]		us-gaap:ValuationTechniqueDiscountedCashFlowMember	us-gaap:ValuationTechniqueDiscountedCashFlowMember	us-gaap:ValuationTechniqueDiscountedCashFlowMember
Debt Instrument, Measurement Input [Extensible List]		us-gaap:MeasurementInputDiscountRateMember	us-gaap:MeasurementInputDiscountRateMember	us-gaap:MeasurementInputDiscountRateMember
Junior Subordinated Notes, at Fair Value | Significant Unobservable Inputs (Level 3) | Minimum
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Discount rate		0.3061	0.3061	0.1801
Junior Subordinated Notes, at Fair Value | Significant Unobservable Inputs (Level 3) | Maximum
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Discount rate		0.3068	0.3068	0.1821

[1] During the year ended December 31, 2017, there were no transfers between Level 1 and Level 2, and there were no transfers into and/or out of Level 3.