Collateral Positions (Details 2) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012	Sep. 30, 2012 U.S. Treasury securities	Sep. 30, 2012 Agency MBS	Sep. 30, 2012 Agency MBS Fannie Mae.	Sep. 30, 2012 Agency MBS Freddie Mac.	Sep. 30, 2012 Agency MBS Ginnie Mae.	Sep. 30, 2012 Non-Agency MBS	Sep. 30, 2012 Non-Agency MBS Rated AAA	Sep. 30, 2012 Non-Agency MBS Rated A	Sep. 30, 2012 Non-Agency MBS Rated BBB	Sep. 30, 2012 Non-Agency MBS Rated BB	Sep. 30, 2012 Non-Agency MBS Rated B	Sep. 30, 2012 Non-Agency MBS Rated CCC	Sep. 30, 2012 Non-Agency MBS Rated CC	Sep. 30, 2012 Non-Agency MBS Rated C	Sep. 30, 2012 Non-Agency MBS D-rated	Sep. 30, 2011 Non-Agency MBS Not Rated	Sep. 30, 2012 Repurchase Agreement Borrowings	Sep. 30, 2012 Repurchase Agreement Borrowings U.S. Treasury securities	Sep. 30, 2012 Repurchase Agreement Borrowings Agency MBS	Sep. 30, 2012 Repurchase Agreement Borrowings Agency MBS Fannie Mae.	Sep. 30, 2012 Repurchase Agreement Borrowings Agency MBS Freddie Mac.	Sep. 30, 2012 Repurchase Agreement Borrowings Agency MBS Ginnie Mae.	Sep. 30, 2012 Repurchase Agreement Borrowings Non-Agency MBS	Sep. 30, 2012 Repurchase Agreement Borrowings Non-Agency MBS Rated AAA	Sep. 30, 2012 Repurchase Agreement Borrowings Non-Agency MBS Rated A	Sep. 30, 2012 Repurchase Agreement Borrowings Non-Agency MBS Rated BBB	Sep. 30, 2012 Repurchase Agreement Borrowings Non-Agency MBS Rated BB	Sep. 30, 2012 Repurchase Agreement Borrowings Non-Agency MBS Rated B	Sep. 30, 2012 Repurchase Agreement Borrowings Non-Agency MBS Rated CCC	Sep. 30, 2012 Repurchase Agreement Borrowings Non-Agency MBS Rated CC	Sep. 30, 2012 Repurchase Agreement Borrowings Non-Agency MBS Rated C	Sep. 30, 2012 Repurchase Agreement Borrowings Non-Agency MBS D-rated	Sep. 30, 2012 Repurchase Agreement Borrowings Non-Agency MBS Not Rated	Sep. 30, 2012 Derivative contracts	Sep. 30, 2011 Derivative contracts Agency MBS	Sep. 30, 2012 Derivative contracts Agency MBS Fannie Mae.	Sep. 30, 2012 Derivative contracts Agency MBS Freddie Mac.	Sep. 30, 2012 Derivative contracts Agency MBS Ginnie Mae.
Collateral Positions
Assets Pledged																		$ 10,544,383	$ 509,704	$ 6,818,804	$ 6,254,273	$ 562,372	$ 2,159	$ 3,215,875	$ 33,619	$ 21,164	$ 13,442	$ 330,200	$ 99,176	$ 273,113	$ 237,426	$ 171,079	$ 668,121	$ 1,368,535	$ 84,150	$ 84,150	$ 65,883	$ 8,949	$ 9,318
Amortized Cost																		9,937,541	513,316	6,573,212	6,032,905	538,205	2,102	2,851,013	32,534	22,217	12,337	307,753	89,421	245,188	215,418	156,944	609,303	1,159,898	80,458	80,458	62,901	8,563	8,994
Accrued Interest on Pledged MBS																		36,116		19,874	17,715	2,156	3	16,242	108	59	61	1,187	327	1,066	1,090	910	3,629	7,805	237	237	185	37	15
Total Fair Value of MBS Pledged and Accrued Interest	$ 10,664,886	$ 509,704	$ 6,923,065	$ 6,338,056	$ 573,514	$ 11,495	$ 3,232,117	$ 33,727	$ 21,223	$ 13,503	$ 331,387	$ 99,503	$ 274,179	$ 238,516	$ 171,989	$ 671,750	$ 1,376,340