Investments In Securities - Trading Securities, Continuous Unrealized Loss Position (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Agency Securities
Fair Value
Less than 12 months, fair value	$ 831,339
12 months or more, fair value	0
Total, fair value	831,339
Unrealized Losses
Less than 12 months, unrealized loss	(2,653)
12 months or more, unrealized loss	0
Total, unrealized loss	$ (2,653)
Credit Risk and Non-Agency Securities
Fair Value
Less than 12 months, fair value		$ 362
12 months or more, fair value		0
Total, fair value		362
Unrealized Losses
Less than 12 months, unrealized loss		(3)
12 months or more, unrealized loss		0
Total, unrealized loss		$ (3)