Interest Receivable (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Interest receivable by investment category
Interest receivable	$ 44,980	$ 42,837
Total MBS
Interest receivable by investment category
Interest receivable	44,979	42,835
Fannie Mae.
Interest receivable by investment category
Interest receivable	18,881	19,774
Freddie Mac.
Interest receivable by investment category
Interest receivable	2,425	3,179
Ginnie Mae.
Interest receivable by investment category
Interest receivable	24	32
Non-Agency MBS
Interest receivable by investment category
Interest receivable	23,649	19,850
Money market investments
Interest receivable by investment category
Interest receivable	$ 1	$ 2