Fair Value of Financial Instruments (Details) (USD $)	Jun. 30, 2011	Dec. 31, 2010
Assets:
Agency MBS	$ 7,295,275,000	$ 5,980,623,000
Non-Agency MBS, including MBS transferred to consolidated VIEs	3,964,279,000	2,078,087,000
Linked Transactions	60,022,000	179,915,000
Derivative hedging instruments	1,843,000
Total assets carried at fair value	11,321,419,000
Liabilities:
Derivative hedging instruments	125,320,000	139,142,000
Recurring basis | Level 2
Assets:
Agency MBS	7,295,275,000
Non-Agency MBS, including MBS transferred to consolidated VIEs	3,964,279,000
Linked Transactions	60,022,000
Derivative hedging instruments	1,843,000
Total assets carried at fair value	11,321,419,000
Liabilities:
Derivative hedging instruments	125,320,000
Total liabilities carried at fair value	125,320,000
Recurring basis | Estimated fair value
Assets:
Agency MBS	7,295,275,000
Non-Agency MBS, including MBS transferred to consolidated VIEs	3,964,279,000
Linked Transactions	60,022,000
Derivative hedging instruments	1,843,000
Total assets carried at fair value	11,321,419,000
Liabilities:
Derivative hedging instruments	125,320,000
Total liabilities carried at fair value	$ 125,320,000