Securities (Details 1) (USD $) In Thousands	9 Months Ended	12 Months Ended
Sep. 30, 2011	Dec. 31, 2010
Amortized cost and estimated fair market value of investment securities and mortgage-backed securities held to maturity
Estimated Fair Market Value	$ 1,647,340	$ 3,867,488
Mortgage-backed securities [Member]
Amortized cost and estimated fair market value of investment securities and mortgage-backed securities held to maturity
Amortized Cost	4,533,557	5,914,372
Gross Unrealized Gains	276,664	285,167
Gross Unrealized Losses	(3)	(32)
Estimated Fair Market Value	4,810,218	6,199,507
Mortgage-backed securities [Member] \| GNMA pass-through certificates [Member]
Amortized cost and estimated fair market value of investment securities and mortgage-backed securities held to maturity
Amortized Cost	90,787	98,887
Gross Unrealized Gains	3,329	2,802
Estimated Fair Market Value	94,116	101,689
Mortgage-backed securities [Member] \| FNMA pass-through certificates [Member]
Amortized cost and estimated fair market value of investment securities and mortgage-backed securities held to maturity
Amortized Cost	1,284,103	1,622,994
Gross Unrealized Gains	85,437	87,271
Gross Unrealized Losses	(3)
Estimated Fair Market Value	1,369,537	1,710,265
Mortgage-backed securities [Member] \| FHLMC pass-through certificates [Member]
Amortized cost and estimated fair market value of investment securities and mortgage-backed securities held to maturity
Amortized Cost	2,322,017	2,943,565
Gross Unrealized Gains	134,388	148,248
Estimated Fair Market Value	2,456,405	3,091,813
Mortgage-backed securities [Member] \| FHLMC and FNMA - REMICs [Member]
Amortized cost and estimated fair market value of investment securities and mortgage-backed securities held to maturity
Amortized Cost	836,650	1,248,926
Gross Unrealized Gains	53,510	46,846
Gross Unrealized Losses		(32)
Estimated Fair Market Value	890,160	1,295,740
Investment Securities [Member]
Amortized cost and estimated fair market value of investment securities and mortgage-backed securities held to maturity
Amortized Cost	1,638,954	3,939,006
Gross Unrealized Gains	8,386	3,698
Gross Unrealized Losses		(75,216)
Estimated Fair Market Value	1,647,340	3,867,488
Investment Securities [Member] \| United States government-sponsored enterprise debt [Member]
Amortized cost and estimated fair market value of investment securities and mortgage-backed securities held to maturity
Amortized Cost	1,638,954	3,939,006
Gross Unrealized Gains	8,386	3,698
Gross Unrealized Losses		(75,216)
Estimated Fair Market Value	$ 1,647,340	$ 3,867,488

Held to Maturity Securities.

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- Definition

This item represents the total of all debt securities grouped by maturity dates, at fair value, which are categorized as held-to-maturity.

+ Details

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- Definition

This item represents the total of all debt securities grouped by maturity dates, at cost, net of adjustments made for accretion, amortization, other-than-temporary impairments, and hedging, if any, which are classified as held-to-maturity.

+ References

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 115

-Paragraph 20

+ Details

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- Definition

As of the balance sheet date, the excess of fair value over carrying value (amortized cost) of a debt security categorized as held-to-maturity, exclusive of dividend or interest income recognized but not yet received and exclusive of any write-downs for other-than-temporary impairment. Such item represents the gross unrecognized holding gain.

+ References

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 115

-Paragraph 19

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 115

-Paragraph 137

+ Details

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- Definition

As of the balance sheet date, the excess of carrying value (amortized cost) over fair value of a debt security categorized as held-to-maturity, exclusive of dividend or interest income recognized but not yet received and exclusive of any write-downs for other-than-temporary impairment. Such item represents the gross unrecognized holding loss.

+ References

+ Details

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