Carrying Amount and Fair Value of Financial Instruments (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Assets
Derivative assets	$ 11
Liabilities
Junior subordinated notes	8,121	$ 11,822
Warrants and investor SARs		30,400
Carrying Amount
Assets
Total investment in mortgages and loans, net	1,255,723	1,280,285
Cash and cash equivalents	53,380	110,531
Restricted cash	157,914	190,179
Derivative assets	11	206
Carrying Amount \| Warrants and investor SARs
Liabilities
Warrants and investor SARs		30,400
Carrying Amount \| Recourse Indebtedness \| 7.0% convertible senior notes
Liabilities
Convertible senior notes	833	831
Carrying Amount \| Recourse Indebtedness \| 4.0% convertible senior notes
Liabilities
Convertible senior notes	106,800	120,271
Carrying Amount \| Recourse Indebtedness \| 7.625% senior notes due 2024
Liabilities
Indebtedness	54,867	55,568
Carrying Amount \| Recourse Indebtedness \| 7.125% Senior Notes due 2019
Liabilities
Indebtedness	67,474	69,188
Carrying Amount \| Recourse Indebtedness \| Senior Secured Notes
Liabilities
Indebtedness	11,063	58,233
Carrying Amount \| Recourse Indebtedness \| Junior subordinated notes, at amortized cost
Liabilities
Junior subordinated notes	25,100	25,100
Carrying Amount \| Non Recourse Indebtedness \| CDO notes payable, at amortized cost
Liabilities
Notes payable	254,724	534,501
Carrying Amount \| Non Recourse Indebtedness \| Loan Payable On Real Estate
Liabilities
Loans payable on real estate	61,922	185,668
Carrying Amount \| Other indebtedness
Liabilities
Indebtedness	40,955	23,915
Carrying Amount \| CMBS securitizations \| Non Recourse Indebtedness
Liabilities
Notes payable	736,586	641,077
Estimated Fair Value
Assets
Total investment in mortgages and loans, net	1,252,780	1,256,342
Cash and cash equivalents	53,380	110,531
Restricted cash	157,914	190,179
Derivative assets	11	206
Estimated Fair Value \| Warrants and investor SARs
Liabilities
Warrants and investor SARs		30,400
Estimated Fair Value \| Recourse Indebtedness \| 7.0% convertible senior notes
Liabilities
Convertible senior notes	533	890
Estimated Fair Value \| Recourse Indebtedness \| 4.0% convertible senior notes
Liabilities
Convertible senior notes	103,457	116,861
Estimated Fair Value \| Recourse Indebtedness \| 7.625% senior notes due 2024
Liabilities
Indebtedness	43,009	53,231
Estimated Fair Value \| Recourse Indebtedness \| 7.125% Senior Notes due 2019
Liabilities
Indebtedness	61,567	69,118
Estimated Fair Value \| Recourse Indebtedness \| Senior Secured Notes
Liabilities
Indebtedness	11,197	62,620
Estimated Fair Value \| Recourse Indebtedness \| Junior subordinated notes, at amortized cost
Liabilities
Junior subordinated notes	8,849	13,099
Estimated Fair Value \| Non Recourse Indebtedness \| CDO notes payable, at amortized cost
Liabilities
Notes payable	196,212	477,032
Estimated Fair Value \| Non Recourse Indebtedness \| Loan Payable On Real Estate
Liabilities
Loans payable on real estate	64,377	188,525
Estimated Fair Value \| Other indebtedness
Liabilities
Indebtedness	40,830	24,321
Estimated Fair Value \| CMBS securitizations \| Non Recourse Indebtedness
Liabilities
Notes payable	744,359	646,642
Junior subordinated notes, at fair value \| Carrying Amount \| Recourse Indebtedness
Liabilities
Junior subordinated notes	8,121	11,822
Junior subordinated notes, at fair value \| Estimated Fair Value \| Recourse Indebtedness
Liabilities
Junior subordinated notes	8,121	11,822
Secured warehouse facilities \| Carrying Amount \| Recourse Indebtedness
Liabilities
Indebtedness	21,743	24,908
Secured warehouse facilities \| Estimated Fair Value \| Recourse Indebtedness
Liabilities
Indebtedness	$ 22,313	$ 26,421

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