Fair Value Hierarchy for Financial Instruments Not Fair Value but For Which Fair Value Is Required To Be Disclosed (Detail) - USD ($) $ in Thousands	Dec. 31, 2018		Dec. 31, 2017
Fair Value Measurement Inputs Disclosure [Line Items]
Junior subordinated notes	$ 6,110		$ 8,121
Significant Unobservable Inputs (Level 3)
Fair Value Measurement Inputs Disclosure [Line Items]
Junior subordinated notes	$ 6,110	[1]	$ 8,121	[2]
Total investment in mortgage loans, held for investment, net, Valuation Technique	us-gaap:ValuationTechniqueDiscountedCashFlowMember		us-gaap:ValuationTechniqueDiscountedCashFlowMember
Investment in mortgage loans, held for sale, Valuation Technique	us-gaap:ValuationTechniqueDiscountedCashFlowMember
Other indebtedness | Significant Unobservable Inputs (Level 3)
Fair Value Measurement Inputs Disclosure [Line Items]
Indebtedness, Valuation Technique			us-gaap:ValuationTechniqueDiscountedCashFlowMember
CMBS securitizations | Significant Unobservable Inputs (Level 3)
Fair Value Measurement Inputs Disclosure [Line Items]
Indebtedness, Valuation Technique	us-gaap:ValuationTechniqueDiscountedCashFlowMember		us-gaap:ValuationTechniqueDiscountedCashFlowMember
7.625% senior notes due 2024 | Significant Other Observable Inputs (Level 2)
Fair Value Measurement Inputs Disclosure [Line Items]
Indebtedness, Valuation Technique	ras:ValuationTechniqueTradingPricingMember		ras:ValuationTechniqueTradingPricingMember
7.125% Senior Notes due 2019 | Significant Other Observable Inputs (Level 2)
Fair Value Measurement Inputs Disclosure [Line Items]
Indebtedness, Valuation Technique	ras:ValuationTechniqueTradingPricingMember		ras:ValuationTechniqueTradingPricingMember
Senior Secured Notes | Significant Unobservable Inputs (Level 3)
Fair Value Measurement Inputs Disclosure [Line Items]
Indebtedness, Valuation Technique			us-gaap:ValuationTechniqueDiscountedCashFlowMember
Junior subordinated notes, at amortized cost | Significant Unobservable Inputs (Level 3)
Fair Value Measurement Inputs Disclosure [Line Items]
Indebtedness, Valuation Technique	us-gaap:ValuationTechniqueDiscountedCashFlowMember		us-gaap:ValuationTechniqueDiscountedCashFlowMember
CDO notes payable, at amortized cost | Significant Unobservable Inputs (Level 3)
Fair Value Measurement Inputs Disclosure [Line Items]
Indebtedness, Valuation Technique	us-gaap:ValuationTechniqueDiscountedCashFlowMember		us-gaap:ValuationTechniqueDiscountedCashFlowMember
Loan Payable On Real Estate | Significant Unobservable Inputs (Level 3)
Fair Value Measurement Inputs Disclosure [Line Items]
Indebtedness, Valuation Technique	us-gaap:ValuationTechniqueDiscountedCashFlowMember		us-gaap:ValuationTechniqueDiscountedCashFlowMember
7.0% convertible senior notes | Significant Other Observable Inputs (Level 2)
Fair Value Measurement Inputs Disclosure [Line Items]
Indebtedness, Valuation Technique			ras:ValuationTechniqueTradingPricingMember
4.0% convertible senior notes | Significant Other Observable Inputs (Level 2)
Fair Value Measurement Inputs Disclosure [Line Items]
Indebtedness, Valuation Technique			ras:ValuationTechniqueTradingPricingMember
Carrying Amount
Fair Value Measurement Inputs Disclosure [Line Items]
Total investment in mortgage loans, held for investment, net	$ 480,061		$ 1,255,723
Investment in mortgage loans, held for sale	4,873
Carrying Amount | Other indebtedness
Fair Value Measurement Inputs Disclosure [Line Items]
Indebtedness			40,955
Carrying Amount | CMBS securitizations
Fair Value Measurement Inputs Disclosure [Line Items]
Notes payable	318,008		736,586
Carrying Amount | 7.625% senior notes due 2024
Fair Value Measurement Inputs Disclosure [Line Items]
Indebtedness	55,100		54,867
Carrying Amount | 7.125% Senior Notes due 2019
Fair Value Measurement Inputs Disclosure [Line Items]
Indebtedness	64,997		67,474
Carrying Amount | Senior Secured Notes
Fair Value Measurement Inputs Disclosure [Line Items]
Indebtedness			11,063
Carrying Amount | Junior subordinated notes, at amortized cost
Fair Value Measurement Inputs Disclosure [Line Items]
Junior subordinated notes	25,100		25,100
Carrying Amount | CDO notes payable, at amortized cost
Fair Value Measurement Inputs Disclosure [Line Items]
Notes payable	116,102		254,724
Carrying Amount | Loan Payable On Real Estate
Fair Value Measurement Inputs Disclosure [Line Items]
Loans payable on real estate	40,499		61,922
Carrying Amount | 7.0% convertible senior notes
Fair Value Measurement Inputs Disclosure [Line Items]
Convertible senior notes			833
Carrying Amount | 4.0% convertible senior notes
Fair Value Measurement Inputs Disclosure [Line Items]
Convertible senior notes			106,800
Estimated Fair Value
Fair Value Measurement Inputs Disclosure [Line Items]
Total investment in mortgage loans, held for investment, net	444,962		1,252,780
Investment in mortgage loans, held for sale	4,873
Estimated Fair Value | Significant Unobservable Inputs (Level 3)
Fair Value Measurement Inputs Disclosure [Line Items]
Total investment in mortgage loans, held for investment, net	444,962		1,252,780
Investment in mortgage loans, held for sale	4,873
Estimated Fair Value | Other indebtedness | Significant Unobservable Inputs (Level 3)
Fair Value Measurement Inputs Disclosure [Line Items]
Indebtedness			40,830
Estimated Fair Value | CMBS securitizations | Significant Unobservable Inputs (Level 3)
Fair Value Measurement Inputs Disclosure [Line Items]
Notes payable	320,711		744,359
Estimated Fair Value | 7.625% senior notes due 2024 | Significant Other Observable Inputs (Level 2)
Fair Value Measurement Inputs Disclosure [Line Items]
Indebtedness	41,229		43,009
Estimated Fair Value | 7.125% Senior Notes due 2019 | Significant Other Observable Inputs (Level 2)
Fair Value Measurement Inputs Disclosure [Line Items]
Indebtedness	58,010		61,567
Estimated Fair Value | Senior Secured Notes | Significant Unobservable Inputs (Level 3)
Fair Value Measurement Inputs Disclosure [Line Items]
Indebtedness			11,197
Estimated Fair Value | Junior subordinated notes, at amortized cost | Significant Unobservable Inputs (Level 3)
Fair Value Measurement Inputs Disclosure [Line Items]
Junior subordinated notes	6,550		8,849
Estimated Fair Value | CDO notes payable, at amortized cost | Significant Unobservable Inputs (Level 3)
Fair Value Measurement Inputs Disclosure [Line Items]
Notes payable	94,513		196,212
Estimated Fair Value | Loan Payable On Real Estate | Significant Unobservable Inputs (Level 3)
Fair Value Measurement Inputs Disclosure [Line Items]
Loans payable on real estate	$ 40,608		64,377
Estimated Fair Value | 7.0% convertible senior notes | Significant Other Observable Inputs (Level 2)
Fair Value Measurement Inputs Disclosure [Line Items]
Convertible senior notes			533
Estimated Fair Value | 4.0% convertible senior notes | Significant Other Observable Inputs (Level 2)
Fair Value Measurement Inputs Disclosure [Line Items]
Convertible senior notes			$ 103,457

[1] During the year ended December 31, 2018, there were no transfers between Level 1 and Level 2, and there were no transfers into and/or out of Level 3.

[2] 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.