Derivative Instruments, Realized Gain (Loss) Related to Derivatives (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Derivative, Gain (Loss) on Derivative, Net [Abstract]
Realized gain (loss) on derivatives, net	$ 12,627	$ (707)	$ 4,786	$ (2,727)
Not Designated as Hedging Instrument [Member]
Derivative, Gain (Loss) on Derivative, Net [Abstract]
Realized gain (loss) on derivatives, net	12,627	(707)	4,786	(2,727)
Not Designated as Hedging Instrument [Member] | Realized Gain (Loss) on Derivatives, Net [Member] | Interest Rate Swaps [Member]
Derivative, Gain (Loss) on Derivative, Net [Abstract]
Realized gain (loss) on derivatives, net	(3,560)	(377)	(17,142)	(961)
Not Designated as Hedging Instrument [Member] | Realized Gain (Loss) on Derivatives, Net [Member] | Swaptions [Member]
Derivative, Gain (Loss) on Derivative, Net [Abstract]
Realized gain (loss) on derivatives, net	(194)	(459)	(1,338)	(834)
Not Designated as Hedging Instrument [Member] | Realized Gain (Loss) on Derivatives, Net [Member] | TBAs [Member]
Derivative, Gain (Loss) on Derivative, Net [Abstract]
Realized gain (loss) on derivatives, net	2,253	(435)	3,340	(1,013)
Not Designated as Hedging Instrument [Member] | Realized Gain (Loss) on Derivatives, Net [Member] | Treasury Futures [Member]
Derivative, Gain (Loss) on Derivative, Net [Abstract]
Realized gain (loss) on derivatives, net	$ 14,128	$ 564	$ 19,926	$ 81