Gross Gains and Losses from Investment Sales (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Gains Losses On Investments [Line Items]
Net realized gain (loss) on sale of mortgage-backed securities	$ (68,679)	$ (225,635)	$ 8,802	$ 2,500	$ 39,103	$ 10,534	$ 12,205	$ 2,505	$ (283,012)	$ 64,347	$ 20,576
Mortgage Backed Securities
Gains Losses On Investments [Line Items]
Gross gains on MBS									18,717	66,084	22,135
Gross losses on MBS									$ (301,729)	$ (1,737)	$ (1,559)