Securitization Transactions (Schedule of CLO Securitization Transactions) (Details) - USD ($) $ in Thousands	6 Months Ended	12 Months Ended
	Jun. 30, 2019	Dec. 31, 2018
Securitization Transactions [Line Items]
Fair Value		$ 2,939,311
Securities, at fair value	$ 1,668,677
CLO I Securitization [Member]
Securitization Transactions [Line Items]
CLO Pricing Date	2018-08	2017-05
CLO Closing Date	2018-08	2017-06
Total Face Amount of Notes Issued	$ 461,840	$ 373,550
Face Amount of Notes Initially Purchased	36,579	36,606
Aggregate Purchase Price of Notes Initially Purchased	$ 25,622	$ 35,926
Reset CLO I Securitization [Member]
Securitization Transactions [Line Items]
CLO Pricing Date		2018-08
CLO Closing Date		2018-08
Total Face Amount of Notes Issued		$ 461,840
Face Amount of Notes Initially Purchased		36,579
Aggregate Purchase Price of Notes Initially Purchased		$ 25,622
CLO II Securitization [Member]
Securitization Transactions [Line Items]
CLO Pricing Date	2017-12	2017-12
CLO Closing Date	2018-01	2018-01
Total Face Amount of Notes Issued	$ 452,800	$ 452,800
Face Amount of Notes Initially Purchased	18,223	18,223
Aggregate Purchase Price of Notes Initially Purchased	$ 16,621	$ 16,621
CLO III Securitization [Member]
Securitization Transactions [Line Items]
CLO Pricing Date	2018-06	2018-06
CLO Closing Date	2018-07	2018-07
Total Face Amount of Notes Issued	$ 407,100	$ 407,100
Face Amount of Notes Initially Purchased	35,480	35,480
Aggregate Purchase Price of Notes Initially Purchased	$ 32,394	32,394
CLO IV Securitization [Member]
Securitization Transactions [Line Items]
CLO Pricing Date	2019-02
CLO Closing Date	2019-03
Total Face Amount of Notes Issued	$ 478,488
Face Amount of Notes Initially Purchased	12,700
Aggregate Purchase Price of Notes Initially Purchased	10,618
CLOs
Securitization Transactions [Line Items]
Fair Value		123,893
CLOs | CLO I Securitization [Member]
Securitization Transactions [Line Items]
Fair Value		0
Securities, at fair value	16,090
CLOs | Reset CLO I Securitization [Member]
Securitization Transactions [Line Items]
Fair Value		16,973
CLOs | CLO II Securitization [Member]
Securitization Transactions [Line Items]
Fair Value		14,721
Securities, at fair value	13,871
CLOs | CLO III Securitization [Member]
Securitization Transactions [Line Items]
Fair Value		$ 19,071
Securities, at fair value	15,941
CLOs | CLO IV Securitization [Member]
Securitization Transactions [Line Items]
Securities, at fair value	$ 10,110