Securitization Transactions Narrative (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2017		Dec. 31, 2016
Securitization Transactions [Line Items]
Investments Fair Value		$ 2,071,707		$ 1,505,026
Participation in Multi-Seller Consumer Loan Securitization [Member]
Securitization Transactions [Line Items]
Aggregate unpaid principal balance of loans sold		$ 124,000
Company's share of loans sold		51.00%
Co-participants share of loans sold		49.00%
Gain (Loss) on Securitization of Financial Assets		$ (100)
Senior notes issued in securitization transaction		87,000
Subordinated notes issued in securitization transaction		$ 18,700
Company's initial percentage ownership of jointly owned entity		51.00%
Affiliated co-participants initial percentage ownership of jointly owned entity		49.00%
Company's current percentage ownership of jointly owned entity		75.00%
CLO I Securitization [Member]
Securitization Transactions [Line Items]
Gain (Loss) on Securitization of Financial Assets		$ 200
Notes issued by CLO securitization		$ 373,600
Percentage of unsecured subordinated notes purchased		25.00%
Principal amount of notes purchased from related party CLO securitization		$ 36,600
Cost of notes purchased from related party CLO securitization		$ 35,900
Percentage non-controlling ownership of related party		25.00%
Minimum economic interest required to be retained		5.00%
Economic interest retained		6.00%
CLO II Securitization [Member]
Securitization Transactions [Line Items]
Principal amount of notes purchased from related party CLO securitization		$ 18,200
Cost of notes purchased from related party CLO securitization		16,600
Loan receivable from related party		16,900
The Company [Member] | CLO I Securitization [Member]
Securitization Transactions [Line Items]
Corporate loans transferred into CLO securitization		62,000
Affiliated Entity [Member] | CLO I Securitization [Member]
Securitization Transactions [Line Items]
Corporate loans transferred into CLO securitization		141,700
Collateralized Loan Obligations [Member]
Securitization Transactions [Line Items]
Investments Fair Value		210,816	[1],[2]	44,956	[3],[4]
Collateralized Loan Obligations [Member] | CLO I Securitization [Member]
Securitization Transactions [Line Items]
Investments Fair Value	[1],[2],[5]	24,300
Collateralized Loan Obligations [Member] | CLO II Securitization [Member]
Securitization Transactions [Line Items]
Investments Fair Value	[1],[2],[5]	13,400
Corporate Equity Investments [Member]
Securitization Transactions [Line Items]
Investments Fair Value		37,465	[1],[2]	$ 33,788	[3],[4],[6]
Corporate Equity Investments [Member] | CLO I Securitization [Member]
Securitization Transactions [Line Items]
Investments Fair Value	[1],[2],[7]	$ 5,000
Non-QM loan securitization [Member]
Securitization Transactions [Line Items]
Economic interest retained		5.10%
Notes issued by non-QM securitization trust		$ 141,200
Cost of notes purchased from securitization trust		$ 700
Threshold for exercising Optional Redemption		30.00%
Percentage used to calculate servicing administrator fee		0.03%
Non-QM loan securitization [Member] | The Company [Member]
Securitization Transactions [Line Items]
Non-QM loans transferred into securitization trust		$ 141,200

[1] See Note 2 and Note 3 in Notes to Consolidated Financial Statements.

[2] The table below shows the ratings on the Company's long investments from Moody's, Standard and Poor's, or Fitch, as well as the Company's long investments that were unrated but guaranteed by the Federal National Mortgage Association, the Federal Home Loan Mortgage Corporation, or the Government National Mortgage Association. Ratings tend to be a lagging credit indicator; as a result, the credit quality of the Company's long investment holdings may be lower than the credit quality implied based on the ratings listed below. In situations where an investment has a split rating, the lowest provided rating is used. The ratings descriptions include ratings qualified with a "+," "-," "1," "2," or "3."Rating Description Percent of EquityUnrated but Agency-Guaranteed 160.32%A/A/A 0.81%Baa/BBB/BBB 2.62%Ba/BB/BB or below 68.03%Unrated 101.85%

[3] See Note 2 and Note 3 in Notes to Consolidated Financial Statements.

[4] The table below shows the Company's long investment ratings from Moody's, Standard and Poor's, or Fitch, as well as the Company's long investments that were unrated but guaranteed by the Federal National Mortgage Association, the Federal Home Loan Mortgage Corporation, or the Government National Mortgage Association. Ratings tend to be a lagging credit indicator; as a result, the credit quality of the Company's long investment holdings may be lower than the credit quality implied based on the ratings listed below. In situations where an investment has a split rating, the lowest provided rating is used. The ratings descriptions include ratings qualified with a "+," "-," "1," "2," or "3."Rating Description Percent of EquityUnrated but Agency-Guaranteed 139.27%Aaa/AAA/AAA 0.84%Aa/AA/AA 0.03%A/A/A 0.05%Baa/BBB/BBB 2.60%Ba/BB/BB or below 30.24%Unrated 60.39%

[5] Includes investment in collateralized loan obligation notes in the amount of $37.7 million that were issued and are managed by related parties of the Company. See Note 9 to the Notes to Consolidated Financial Statements.

[6] Conformed to current period presentation.

[7] Represents the Company's investment in a related party. See Note 9 to the Notes to Consolidated Financial Statements.