Summary of Significant Accounting Policies - Narrative (Details)				3 Months Ended					9 Months Ended
	Apr. 06, 2020 USD ($)	Jan. 01, 2020 USD ($)	Jun. 07, 2016	Jun. 30, 2021 USD ($)	Mar. 31, 2021 USD ($)	Sep. 30, 2020 USD ($) $ / shares shares	Jun. 30, 2020 USD ($) $ / shares shares	Mar. 31, 2020 USD ($)	Sep. 30, 2021 USD ($) Segment $ / shares shares	Sep. 30, 2020 USD ($) $ / shares shares	Dec. 31, 2020 USD ($) $ / shares shares	Nov. 19, 2018 USD ($)	Aug. 18, 2017 USD ($)	Apr. 25, 2017 USD ($)
Summary Of Significant Accounting Policies [Line Items]
Amount of loan discount reclassified		$ (10,200,000)
Proceeds from issuance of preferred stock and warrants, net of offering costs	$ 125,000,000								$ 0	$ 124,976,000
Preferred stock, par value per share (in dollars per share) | $ / shares									$ 0.01		$ 0.01
Preferred stock, liquidation preference per share (in dollars per share) | $ / shares						$ 25.00				$ 25.00
Warrant term							5 years
Class of warrant or right, outstanding (in shares) | shares						6,500,000	6,500,000		6,500,000	6,500,000
Investment warrants, exercise price (in dollars per share) | $ / shares							$ 10.00
Warrants original basis							$ 9,500,000		$ 9,500,000
Convertible notes payable				$ 5,000,000	$ 2,500,000	$ 2,500,000	0	$ 8,000,000	$ 0	$ 2,500,000
Payments for repurchase of convertible notes				5,100,000	2,400,000	2,300,000		8,200,000		2,300,000
Convertible senior notes repurchase				$ 0	$ 0	0		$ 81,000
Percentage of incentive fees payable in cash									100.00%
Minimum assets with banking institutions									$ 1,000,000,000
Property held-for-sale									6,100,000		$ 7,800,000
Rental properties									0		700,000
Put option liability									$ 20,843,000		$ 14,205,000
Loans and securities, credit loss expenses						400,000				1,300,000
Loss from loan settlement										700,000
Loan transaction expense						$ 200,000				$ 200,000
Number of operating segments | Segment									1
Restricted stock | Granted in 2021 | Employees
Summary Of Significant Accounting Policies [Line Items]
Vesting period									4 years
Restricted stock | Granted Prior to 2021 | Employees
Summary Of Significant Accounting Policies [Line Items]
Vesting period									3 years
Restricted stock | Share-based Payment Arrangement, Tranche One | Granted in 2021 | Employees
Summary Of Significant Accounting Policies [Line Items]
Percentage of outstanding shares on a fully diluted basis (up to)									25.00%
Restricted stock | Share-based Payment Arrangement, Tranche One | Granted Prior to 2021 | Employees
Summary Of Significant Accounting Policies [Line Items]
Percentage of outstanding shares on a fully diluted basis (up to)									33.33%
Restricted stock | Share-based Payment Arrangement, Tranche Two | Granted in 2021 | Employees
Summary Of Significant Accounting Policies [Line Items]
Percentage of outstanding shares on a fully diluted basis (up to)									25.00%
Restricted stock | Share-based Payment Arrangement, Tranche Two | Granted Prior to 2021 | Employees
Summary Of Significant Accounting Policies [Line Items]
Percentage of outstanding shares on a fully diluted basis (up to)									33.33%
Restricted stock | Share-based Payment Arrangement, Tranche Three | Granted in 2021 | Employees
Summary Of Significant Accounting Policies [Line Items]
Percentage of outstanding shares on a fully diluted basis (up to)									25.00%
Restricted stock | Share-based Payment Arrangement, Tranche Three | Granted Prior to 2021 | Employees
Summary Of Significant Accounting Policies [Line Items]
Percentage of outstanding shares on a fully diluted basis (up to)									33.33%
Restricted stock | Share-based Payment Arrangement, Tranche Four | Granted in 2021 | Employees
Summary Of Significant Accounting Policies [Line Items]
Percentage of outstanding shares on a fully diluted basis (up to)									25.00%
2014 Director Equity Plan
Summary Of Significant Accounting Policies [Line Items]
Number of shares available under for distribution (in shares) | shares									60,000
Percentage of annual retainer received in shares									40.00%
Percentage of annual retainer received in cash									60.00%
2014 Director Equity Plan | Restricted stock
Summary Of Significant Accounting Policies [Line Items]
Annual retainer amount									$ 100,000
Long Term Incentive Plan | Restricted stock | IPO
Summary Of Significant Accounting Policies [Line Items]
Number of restricted stock awards issued to independent directors (in shares) | shares									2,000
2016 Equity Incentive Plan
Summary Of Significant Accounting Policies [Line Items]
Percentage of outstanding shares on a fully diluted basis (up to)			5.00%
2016 Equity Incentive Plan | Share-based Payment Arrangement, Tranche One | Granted in 2021
Summary Of Significant Accounting Policies [Line Items]
Percentage of outstanding shares on a fully diluted basis (up to)			25.00%
2016 Equity Incentive Plan | Share-based Payment Arrangement, Tranche One | Granted Prior to 2021
Summary Of Significant Accounting Policies [Line Items]
Percentage of outstanding shares on a fully diluted basis (up to)			33.33%
2016 Equity Incentive Plan | Share-based Payment Arrangement, Tranche Two | Granted in 2021
Summary Of Significant Accounting Policies [Line Items]
Percentage of outstanding shares on a fully diluted basis (up to)			25.00%
2016 Equity Incentive Plan | Share-based Payment Arrangement, Tranche Two | Granted Prior to 2021
Summary Of Significant Accounting Policies [Line Items]
Percentage of outstanding shares on a fully diluted basis (up to)			33.33%
2016 Equity Incentive Plan | Share-based Payment Arrangement, Tranche Three | Granted in 2021
Summary Of Significant Accounting Policies [Line Items]
Percentage of outstanding shares on a fully diluted basis (up to)			25.00%
2016 Equity Incentive Plan | Share-based Payment Arrangement, Tranche Three | Granted Prior to 2021
Summary Of Significant Accounting Policies [Line Items]
Percentage of outstanding shares on a fully diluted basis (up to)			33.33%
2016 Equity Incentive Plan | Share-based Payment Arrangement, Tranche Four | Granted in 2021
Summary Of Significant Accounting Policies [Line Items]
Percentage of outstanding shares on a fully diluted basis (up to)			25.00%
Servicer | Servicing agreement
Summary Of Significant Accounting Policies [Line Items]
Percentage of fair market value of REO									1.00%
Percentage of purchase price of REO									1.00%
Renewal term									1 year
Thetis Asset Management LLC | Amended and restated management agreement
Summary Of Significant Accounting Policies [Line Items]
Period of common shares held as base management fee (at least)									3 years
Convertible notes payable
Summary Of Significant Accounting Policies [Line Items]
Aggregate principal														$ 87,500,000
Additional aggregate principal												$ 15,900,000	$ 20,500,000
Interest rate														7.25%
Principal amount of note (in dollars per share) | $ / shares									$ 25.00
Cumulative discount									$ 3,200,000
Common stock | Convertible notes payable
Summary Of Significant Accounting Policies [Line Items]
Conversion rate									1.7279
Conversion price (in dollars per share) | $ / shares									$ 14.47
Put option
Summary Of Significant Accounting Policies [Line Items]
Present value of put liability							$ 50,700,000		$ 50,700,000
Put option liability term									39 months
Preferred stock - Series A shares
Summary Of Significant Accounting Policies [Line Items]
Preferred stock, shares issued (in shares) | shares							2,307,400		2,307,400		2,307,400
Preferred stock, fixed-to-floating rate cumulative redeemable							7.25%		7.25%
Preferred stock, par value per share (in dollars per share) | $ / shares							$ 25.00
Preferred stock, liquidation preference per share (in dollars per share) | $ / shares									$ 25.00		$ 25.00
Preferred stock - Series B shares
Summary Of Significant Accounting Policies [Line Items]
Preferred stock, shares issued (in shares) | shares							2,892,600		2,892,600		2,892,600
Preferred stock, fixed-to-floating rate cumulative redeemable							5.00%		5.00%
Preferred stock, par value per share (in dollars per share) | $ / shares							$ 25.00
Preferred stock, liquidation preference per share (in dollars per share) | $ / shares									$ 25.00		$ 25.00
Minimum | Servicer | Servicing agreement
Summary Of Significant Accounting Policies [Line Items]
Servicing fees percentage									0.65%
Maximum
Summary Of Significant Accounting Policies [Line Items]
Estimated useful lives of an assets									27 years 6 months
Maximum | Servicer | Servicing agreement
Summary Of Significant Accounting Policies [Line Items]
Servicing fees percentage									1.25%