Securitization Transactions Schedule of Assets and Liabilities attributable to Consolidated VIEs (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Variable Interest Entity [Line Items]
Cash and cash equivalents	$ 44,656	$ 47,233
Investments Fair Value	2,939,311	2,071,707
Interest and dividends payable	7,159	5,904
Other secured borrowings, at fair value	297,948	125,105
Consolidated Entities [Member]
Variable Interest Entity [Line Items]
Cash and cash equivalents	0	333
Investments Fair Value	314,202	132,424
Interest and Dividends Receivable	3,527	0
Interest and dividends payable	103	333
Other secured borrowings, at fair value	$ 297,948	$ 125,105