Schedule of Mortgage Backed Securities (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended	12 Months Ended
	Mar. 31, 2014	Dec. 31, 2013
Schedule Of Investment Income Reported Amounts By Category [Line Items]
TBA dollar roll securities - Face	$ 3,400,000	$ 600,000
TBA dollar roll securities - Cost	3,565,399	632,270
TBA dollar roll securities - Fair Value	3,551,765	627,187
TBA dollar roll securities - Net Asset (Liability)	$ (13,634)	$ (5,083)