Securities (Details) (USD $) In Thousands	9 Months Ended	12 Months Ended
Sep. 30, 2011	Dec. 31, 2010
Securities available for sale:
Estimated Fair Market Value	$ 9,905,741
Investment Securities [Member]
Securities available for sale:
Amortized Cost	6,767	86,767
Gross Unrealized Gains	641	3,028
Estimated Fair Market Value	7,408	89,795
Investment Securities [Member] \| United States government-sponsored enterprise debt [Member]
Securities available for sale:
Amortized Cost		80,000
Gross Unrealized Gains		2,647
Estimated Fair Market Value		82,647
Investment Securities [Member] \| Equity Securities [Member]
Securities available for sale:
Amortized Cost	6,767	6,767
Gross Unrealized Gains	641	381
Estimated Fair Market Value	7,408	7,148
Mortgage-backed securities [Member]
Securities available for sale:
Amortized Cost	9,748,718	17,925,284
Gross Unrealized Gains	157,132	292,406
Gross Unrealized Losses	(109)	(97,513)
Estimated Fair Market Value	9,905,741	18,120,537
Mortgage-backed securities [Member] \| GNMA pass-through certificates [Member]
Securities available for sale:
Amortized Cost	1,190,293	1,560,755
Gross Unrealized Gains	28,034	27,214
Gross Unrealized Losses	(109)	(7,487)
Estimated Fair Market Value	1,218,218	1,580,482
Mortgage-backed securities [Member] \| FNMA pass-through certificates [Member]
Securities available for sale:
Amortized Cost	4,783,924	10,333,033
Gross Unrealized Gains	61,662	122,305
Gross Unrealized Losses		(57,550)
Estimated Fair Market Value	4,845,586	10,397,788
Mortgage-backed securities [Member] \| FHLMC pass-through certificates [Member]
Securities available for sale:
Amortized Cost	3,685,676	5,521,741
Gross Unrealized Gains	65,366	129,547
Gross Unrealized Losses		(32,116)
Estimated Fair Market Value	3,751,042	5,619,172
Mortgage-backed securities [Member] \| FHLMC and FNMA - REMICs [Member]
Securities available for sale:
Amortized Cost	88,825	509,755
Gross Unrealized Gains	2,070	13,340
Estimated Fair Market Value	$ 90,895	$ 523,095

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This item represents the cost of debt and equity securities, which are categorized neither as held-to-maturity nor trading, net of adjustments made for accretion, amortization, other-than-temporary impairments, and hedging, if any.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name FASB Staff Position (FSP)

-Number FAS115-1/124-1

-Paragraph 7

-Footnote 2

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 115

-Paragraph 19

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- Definition

This item represents the total of all debt securities grouped by maturity dates, at fair value, which are categorized neither as held-to-maturity nor trading securities.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 115

-Paragraph 20

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- Definition

This item represents the gross unrealized gains for securities which are categorized neither as held-to-maturity nor trading securities. Such gross unrealized gains are the excess of the fair value of the Available-for-sale Securities over their carrying value as of the reporting date. Such gross unrealized gains are included in other comprehensive income in the statement of shareholders' equity, unless the Available-for-sale Security is designated as a hedge. All or a portion of the unrealized holding gain of an available-for-sale security that is designated as being hedged in a fair value hedge shall be recognized in earnings during the period of the hedge.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 133

-Paragraph 22

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 115

-Paragraph 13, 19

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- Definition

This item represents the gross unrealized losses for securities which are categorized neither as held-to-maturity nor trading securities. Such gross unrealized losses are the excess of the carrying value of the Available-for-sale Securities over their fair value as of the reporting date. Such gross unrealized losses are included in other comprehensive income in the statement of shareholders' equity, unless the Available-for-sale Security is designated as a hedge or is determined to have had an other than temporary decline in fair value below its amortized cost basis. All or a portion of the unrealized holding loss of an Available-for-sale Security that is designated as being hedged in a fair value hedge shall be recognized in earnings during the period of the hedge, as should other than temporary declines in fair value below costs basis.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 115

-Paragraph 16

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 133

-Paragraph 22

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 115

-Paragraph 13, 19

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