Mortgage Backed Securities Mortgage backed securities designated as Trading (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012	Dec. 31, 2012
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading Securities, Debt	$ 29,034		$ 29,034		$ 30,069
Trading Securities, Amortized cost	27,231		27,231		27,535
Trading Securities, Unrealized Holding Loss	$ (623)	$ 569	$ (731)	$ 0