Interest Receivable (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Interest receivable by investment category
Interest receivable	$ 42,106	$ 44,033
Total MBS
Interest receivable by investment category
Interest receivable	42,084	44,024
Fannie Mae.
Interest receivable by investment category
Interest receivable	16,157	17,597
Freddie Mac.
Interest receivable by investment category
Interest receivable	3,246	2,696
Ginnie Mae.
Interest receivable by investment category
Interest receivable	23	24
Non-Agency MBS
Interest receivable by investment category
Interest receivable	22,658	23,707
Money market and other investments
Interest receivable by investment category
Interest receivable	$ 22	$ 9