Investment in Securities (Unrealized Loss Positions Securities) (Details) $ in Thousands	Sep. 30, 2019 USD ($)
Securities, Available-for-sale [Line Items]
Fair Value, Less than 12 Months	$ 119,036
Unrealized Losses, Less than 12 Months	(2,702)
Fair Value, Greater than 12 Months	234,385
Unrealized Losses, Greater than 12 Months	(5,203)
Fair Value, Total	353,421
Unrealized Loss, Total	(7,905)
Agency RMBS
Securities, Available-for-sale [Line Items]
Fair Value, Less than 12 Months	65,476
Unrealized Losses, Less than 12 Months	(578)
Fair Value, Greater than 12 Months	185,049
Unrealized Losses, Greater than 12 Months	(2,996)
Fair Value, Total	250,525
Unrealized Loss, Total	(3,574)
Non-Agency RMBS
Securities, Available-for-sale [Line Items]
Fair Value, Less than 12 Months	26,133
Unrealized Losses, Less than 12 Months	(842)
Fair Value, Greater than 12 Months	42,111
Unrealized Losses, Greater than 12 Months	(1,852)
Fair Value, Total	68,244
Unrealized Loss, Total	(2,694)
CLOs
Securities, Available-for-sale [Line Items]
Fair Value, Less than 12 Months	17,905
Unrealized Losses, Less than 12 Months	(1,174)
Fair Value, Greater than 12 Months	4,222
Unrealized Losses, Greater than 12 Months	(182)
Fair Value, Total	22,127
Unrealized Loss, Total	(1,356)
Other Securities
Securities, Available-for-sale [Line Items]
Fair Value, Less than 12 Months	9,522
Unrealized Losses, Less than 12 Months	(108)
Fair Value, Greater than 12 Months	3,003
Unrealized Losses, Greater than 12 Months	(173)
Fair Value, Total	12,525
Unrealized Loss, Total	$ (281)