Derivative Instruments and Hedging Activities - Fair Value of Derivative Instruments Not Designated as Hedging Instruments (Details) - USD ($) $ in Thousands		Dec. 31, 2015	Dec. 31, 2014
TBA securities
Derivative [Line Items]
Derivatives not designated as hedging instruments - assets	[1]	$ 226,929	$ 284,971
US Treasury Futures
Derivative [Line Items]
Derivatives not designated as hedging instruments - assets		0	379
Options on US Treasury Futures
Derivative [Line Items]
Derivatives not designated as hedging instruments - assets		15	92
Interest Rate Swap Future
Derivative [Line Items]
Derivatives not designated as hedging instruments - assets		706	0
Derivatives not designated as hedging instruments - liabilities		0	331
Swaption
Derivative [Line Items]
Derivatives not designated as hedging instruments - assets		821	2,273
Eurodollar Future
Derivative [Line Items]
Derivatives not designated as hedging instruments - liabilities		1,242	900
Interest Rate Swap
Derivative [Line Items]
Derivatives not designated as hedging instruments - liabilities	[2]	$ 258	$ 232

[1] Open TBA purchases and sales involving the same counterparty, same underlying deliverable and the same settlement date are reflected in our accompanying consolidated financial statements on a net basis. There was no netting of TBA sales against TBA purchases as of December 31, 2015 and December 31, 2014.

[2] Includes interest rate swaps in our Agency IO portfolio.