Derivative Financial Instruments (Balance Sheet Information) (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Derivatives, Fair Value [Line Items]
Derivative fair value	$ 1,181	$ 669
Investments-trading [Member] | TBAs [Member]
Derivatives, Fair Value [Line Items]
Derivative fair value	55,779	3,686
Investments-trading [Member] | Other Extended Settlement Trades [Member]
Derivatives, Fair Value [Line Items]
Derivative fair value	1
Trading securities sold, not yet purchased [Member] | TBAs [Member]
Derivatives, Fair Value [Line Items]
Derivative fair value	$ (54,599)	$ (3,017)