Securitization Transactions Narrative (Details) - USD ($) $ in Thousands		1 Months Ended	3 Months Ended			12 Months Ended
		Aug. 31, 2016	Mar. 31, 2019		Mar. 31, 2018	Dec. 31, 2018		Dec. 31, 2017
Securitization Transactions [Line Items]
Face amount of notes distributed from Risk Retention Vehicle						$ 5,600
Proceeds received from equity investment in risk retention vehicle (liquidation)						5,700
Minimum economic interest required to be retained					5.00%
TBA securities, at fair value						$ 2,939,311
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%
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			49.60%			62.00%		75.00%
Maximum amount at risk			$ 2,600
CLO I Securitization [Member]
Securitization Transactions [Line Items]
Loss on securitization of financial assets					$ 200
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
CLOs
Securitization Transactions [Line Items]
TBA securities, at fair value						$ 123,893
CLOs | CLO I Securitization [Member]
Securitization Transactions [Line Items]
TBA securities, at fair value	[1],[2]		$ 17,742	[3]		0	[4]
CLOs | Distributed from Risk Retention Vehicle [Member]
Securitization Transactions [Line Items]
TBA securities, at fair value						$ 4,300
Non-QM loan securitization
Securitization Transactions [Line Items]
Threshold for exercising Optional Redemption			30.00%			30.00%
Percentage used to calculate servicing administrator fee			0.03%			0.03%

[1] In August 2018, the notes originally issued by the CLO I Issuer in 2017 were fully redeemed, and the CLO I Issuer simultaneously issued new notes in conjunction with this full redemption.

[2] Included on the Company's Consolidated Condensed Schedule of Investments in Collateralized Loan Obligations.

[3] Includes secured and unsecured subordinated notes.

[4] Excludes the Company's equity investment in the CLO I Risk Retention Vehicle, as discussed above.