Interest Receivable (Details) (USD $) In Thousands	Sep. 30, 2011	Dec. 31, 2010
Interest receivable by investment category
Interest receivable	$ 44,340	$ 38,215
MBS interest receivable
Interest receivable by investment category
Interest receivable	44,337	38,201
Fannie Mae.
Interest receivable by investment category
Interest receivable	20,878	19,669
Freddie Mac.
Interest receivable by investment category
Interest receivable	3,514	3,351
Ginnie Mae.
Interest receivable by investment category
Interest receivable	36	51
Non-Agency MBS
Interest receivable by investment category
Interest receivable	19,909	15,130
Money market investments
Interest receivable by investment category
Interest receivable	$ 3	$ 14