Accumulated Other Comprehensive Income (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning balance accumulated other comprehensive income (loss)	$ 262,854
Other comprehensive income (loss) before reclassifications	(701,899)
Amounts reclassified to net loss on the sale of mortgage-backed securities	23,032
Amounts reclassified to net loss on the sale of mortgage-backed securities	283,012
Amounts reclassified for impairment loss on mortgage-backed securities	8,102
Amounts reclassified to interest expense	116,847
Net current period other comprehensive income (loss)	120,684	(25,476)	(155,902)
Other comprehensive income (loss)	(270,906)	89,532	67,431
Ending balance accumulated other comprehensive income (loss)	(8,052)	262,854
Derivative Instruments
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning balance	(237,599)
Other comprehensive income (loss) before reclassifications	(21,054)
Amount reclassified to mortgage-backed securities available for sale	24,891
Amounts reclassified to interest expense	116,847
Net current period other comprehensive income (loss)	120,684
Ending balance	(116,915)
Available-for-sale Securities
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning balance accumulated other comprehensive income (loss)	499,343
Other comprehensive income (loss) before reclassifications	(680,967)
Amounts reclassified to net loss on the sale of mortgage-backed securities	283,012
Amounts reclassified for impairment loss on mortgage-backed securities	8,102
Net current period other comprehensive income (loss)	(389,853)
Ending balance accumulated other comprehensive income (loss)	109,490
Unsettled Agency Contracts
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning balance accumulated other comprehensive income (loss)	1,217
Other comprehensive income (loss) before reclassifications	642
Amount reclassified to mortgage-backed securities available for sale	(1,859)
Net current period other comprehensive income (loss)	(1,217)
Other Investments
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning balance accumulated other comprehensive income (loss)	(107)
Other comprehensive income (loss) before reclassifications	(520)
Net current period other comprehensive income (loss)	(520)
Ending balance accumulated other comprehensive income (loss)	$ (627)