Investment Securities, at Fair Value - Scheduled Maturity of CMBS (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Fair Value
Total	$ 35,741	$ 40,974
CMBS [Member]
Amortized Cost
Due within one year	0
Due after one year through five years	13,700
Due after five years through 10 years	24,910
Due after 10 years	0
Amortized Cost	38,610	43,006
Fair Value
Due within one year	0
Due after one year through five years	14,112
Due after five years through 10 years	21,629
Due after 10 years	0
Total	$ 35,741	$ 40,974