Interest Receivable (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Interest receivable by investment category
Interest receivable	$ 44,033	$ 42,837
Total MBS
Interest receivable by investment category
Interest receivable	44,024	42,835
Fannie Mae.
Interest receivable by investment category
Interest receivable	17,597	19,774
Freddie Mac.
Interest receivable by investment category
Interest receivable	2,696	3,179
Ginnie Mae.
Interest receivable by investment category
Interest receivable	24	32
Non-Agency MBS
Interest receivable by investment category
Interest receivable	23,707	19,850
Money market and other investments
Interest receivable by investment category
Interest receivable	$ 9	$ 2