Long-Term Debt - Additional Information (Details)		1 Months Ended				3 Months Ended			12 Months Ended
	Dec. 31, 2019 USD ($)	Sep. 30, 2019 USD ($)	Jun. 30, 2018 USD ($) $ / shares	Aug. 31, 2017 USD ($)	Jan. 31, 2016	Sep. 30, 2020 USD ($)	Jun. 30, 2020 USD ($)	Mar. 31, 2020 USD ($)	Dec. 31, 2020 USD ($) $ / shares
Debt Instrument [Line Items]
FHLB transition period					5 years
Repayments of FHLBC borrowings									$ 2,000,000,000.0
Federal home loan bank stock	$ 43,393,000								5,000,000
Accrued interest payable	6,000,000								1,000,000
Accrued interest payable	$ 60,655,000								34,858,000
Convertible notes | Exchangeable Senior Notes Due 2025
Debt Instrument [Line Items]
Debt instrument interest rate		5.75%
Unamortized deferred issuance costs									4,000,000
Convertible notes		$ 201,000,000							$ 172,000,000
Net proceeds from issuance of convertible debt		$ 195,000,000
Interest expense yield		6.30%
Convertible debt, conversion ratio	0.0552644
Convertible senior notes conversion per share (in dollars per share) | $ / shares									$ 18.09
Accrued interest payable									$ 2,000,000
Repurchased debt instrument, face amount							$ 29,000,000
Gain (loss) on extinguishment of debt							6,000,000
Convertible notes | Senior Notes Due 2024
Debt Instrument [Line Items]
Debt instrument interest rate			5.625%
Unamortized deferred issuance costs									2,000,000
Convertible notes			$ 200,000,000						150,000,000
Net proceeds from issuance of convertible debt			$ 194,000,000
Interest expense yield			6.20%
Convertible debt, conversion ratio			0.0548317
Convertible senior notes conversion per share (in dollars per share) | $ / shares			$ 18.24
Accrued interest payable									4,000,000
Repurchased debt instrument, face amount							50,000,000
Gain (loss) on extinguishment of debt							9,000,000
Percent of par at issuance			99.50%
Debt discount									500,000
Convertible notes | Senior Notes Due 2023
Debt Instrument [Line Items]
Debt instrument interest rate				4.75%
Unamortized deferred issuance costs									3,000,000
Convertible notes				$ 245,000,000					$ 199,000,000
Net proceeds from issuance of convertible debt				$ 238,000,000
Interest expense yield				5.30%
Convertible debt, conversion ratio				0.0544764
Convertible senior notes conversion per share (in dollars per share) | $ / shares									$ 18.36
Accrued interest payable									$ 4,000,000
Repurchased debt instrument, face amount							46,000,000
Gain (loss) on extinguishment of debt							10,000,000
Trust Preferred Securities
Debt Instrument [Line Items]
Long-term debt, net									$ 100,000,000
Trust Preferred Securities | LIBOR
Debt Instrument [Line Items]
Basis spread on variable rate									2.25%
Subordinated Notes
Debt Instrument [Line Items]
Long-term debt, net									$ 40,000,000
Trust Preferred Securities and Subordinated Notes
Debt Instrument [Line Items]
Accrued interest payable	$ 1,000,000								1,000,000
Line of Credit | Non-Recourse Business Purpose Loan Financing Facility Two
Debt Instrument [Line Items]
Long-term debt, net									114,000,000
Long-term debt, gross									115,000,000
Unamortized deferred issuance costs									1,000,000
Line of Credit | Non-Recourse Business Purpose Loan Financing Facility Two | LIBOR
Debt Instrument [Line Items]
Basis spread on variable rate						3.85%
Variable rate, floor (as a percent)						0.50%
Line of Credit | Non-Recourse Business Purpose Loan Financing Facility One
Debt Instrument [Line Items]
Long-term debt, net									249,000,000
Long-term debt, gross									252,000,000
Unamortized deferred issuance costs									2,000,000
Maximum borrowing capacity							372,000,000
Line of Credit | Non-Recourse Business Purpose Loan Financing Facility One | Secured Debt [Member]
Debt Instrument [Line Items]
Maximum borrowing capacity							197,000,000
Line of Credit | Non-Recourse Business Purpose Loan Financing Facility One | Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Maximum borrowing capacity							$ 175,000,000
Line of Credit | Non-Recourse Business Purpose Loan Financing Facility One | LIBOR
Debt Instrument [Line Items]
Basis spread on variable rate							7.50%
Variable rate, floor (as a percent)							1.50%
Line of Credit | Recourse Business Purpose Loan Financing Facility Through September 2023
Debt Instrument [Line Items]
Long-term debt, net									80,000,000
Long-term debt, gross									80,000,000
Unamortized deferred issuance costs									200,000
Pledged assets real estate pledged as collateral, at fair value									106,000,000
Maximum borrowing capacity						$ 250,000,000
Line of Credit | Recourse Business Purpose Loan Financing Facility Through September 2023 | LIBOR
Debt Instrument [Line Items]
Basis spread on variable rate						3.00%
Line of Credit | Recourse Business Purpose Loan Financing Facility
Debt Instrument [Line Items]
Long-term debt, net									51,000,000
Long-term debt, gross									52,000,000
Unamortized deferred issuance costs									500,000
Maximum borrowing capacity							$ 350,000,000
Line of Credit | Recourse Business Purpose Loan Financing Facility | LIBOR
Debt Instrument [Line Items]
Variable rate, floor (as a percent)							1.00%
Line of Credit | Recourse Business Purpose Loan Financing Facility | LIBOR | Minimum
Debt Instrument [Line Items]
Basis spread on variable rate							3.00%
Line of Credit | Recourse Business Purpose Loan Financing Facility | LIBOR | Maximum
Debt Instrument [Line Items]
Basis spread on variable rate							3.50%
Line of Credit | Recourse Revolving Debt Facility
Debt Instrument [Line Items]
Long-term debt, gross									0
Maximum borrowing capacity								$ 50,000,000
Line of Credit | Recourse Revolving Debt Facility | LIBOR
Debt Instrument [Line Items]
Basis spread on variable rate								3.00%
Bridge Loan | Non-Recourse Business Purpose Loan Financing Facility Two
Debt Instrument [Line Items]
Pledged assets real estate pledged as collateral, at fair value									186,000,000
Bridge Loan | Non-Recourse Business Purpose Loan Financing Facility One
Debt Instrument [Line Items]
Pledged assets real estate pledged as collateral, at fair value									338,000,000
Bridge Loan | Recourse Business Purpose Loan Financing Facility
Debt Instrument [Line Items]
Pledged assets real estate pledged as collateral, at fair value									24,000,000
Loans Payable [Member] | Non-Recourse Business Purpose Loan Financing Facility One
Debt Instrument [Line Items]
Pledged assets real estate pledged as collateral, at fair value									21,000,000
Loans Payable [Member] | Recourse Business Purpose Loan Financing Facility
Debt Instrument [Line Items]
Pledged assets real estate pledged as collateral, at fair value									49,000,000
Affiliated Entity | Recourse Subordinate Securities Financing Facilities [Member] | Non-Marginable Debt Repurchase Agreement One
Debt Instrument [Line Items]
Debt instrument interest rate	4.21%
Long-term debt, net									177,000,000
Long-term debt, gross									178,000,000
Unamortized deferred issuance costs									1,000,000
Affiliated Entity | Recourse Subordinate Securities Financing Facilities [Member] | Non-Marginable Debt Repurchase Agreement Two
Debt Instrument [Line Items]
Debt instrument interest rate						4.21%
Long-term debt, net									102,000,000
Long-term debt, gross									103,000,000
Unamortized deferred issuance costs									1,000,000
Affiliated Entity | Sequoia Choice | Recourse Subordinate Securities Financing Facilities [Member] | Non-Marginable Debt Repurchase Agreement One
Debt Instrument [Line Items]
Pledged assets real estate pledged as collateral, at fair value									249,000,000
Affiliated Entity | CAFL | Recourse Subordinate Securities Financing Facilities [Member] | Non-Marginable Debt Repurchase Agreement Two
Debt Instrument [Line Items]
Pledged assets real estate pledged as collateral, at fair value									114,000,000
FHLB Chicago | FHLB Subsidiary
Debt Instrument [Line Items]
Outstanding FHLB advances	$ 2,000,000,000.00								$ 1,000,000
Weighted average interest rate	1.88%								0.30%
Weighted average maturity (in years)	6 years
FHLB Chicago | Redwood | Held-for sale residential loans | Restricted cash
Debt Instrument [Line Items]
Residential mortgage loans securing FHLB advances									$ 1,000,000