Securities (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Securities
Available-for-sale, amortized cost	$ 422,225	$ 330,481
Available-for-sale, Gross Unrealized Gains	6,815	6,510
Available-for-sale, Gross Unrealized Losses	(666)	(691)
Total available-for-sale securities	428,374	336,300
Held-to-maturity, amortized cost	1,709,427	1,700,141
Held-to-maturity, Gross Unrealized Gains	26,275	27,905
Held-to-maturity, Gross Unrealized Losses	(2,976)	(2,956)
Held-to-maturity, estimated fair value	1,732,726	1,725,090
Residential mortgage-backed securities
Securities
Available-for-sale, amortized cost	323,538	231,796
Available-for-sale, Gross Unrealized Gains	6,730	6,296
Available-for-sale, Gross Unrealized Losses	(490)	(671)
Total available-for-sale securities	329,778	237,421
Held-to-maturity, amortized cost	1,627,865	1,699,485
Held-to-maturity, Gross Unrealized Gains	26,141	27,905
Held-to-maturity, Gross Unrealized Losses	(2,914)	(2,956)
Held-to-maturity, estimated fair value	1,651,092	1,724,434
GSE issuance REMICs and CMOs
Securities
Available-for-sale, amortized cost	293,952	200,152
Available-for-sale, Gross Unrealized Gains	5,698	5,258
Available-for-sale, Gross Unrealized Losses	(447)	(583)
Total available-for-sale securities	299,203	204,827
Held-to-maturity, amortized cost	1,622,615	1,693,437
Held-to-maturity, Gross Unrealized Gains	26,039	27,787
Held-to-maturity, Gross Unrealized Losses	(2,913)	(2,955)
Held-to-maturity, estimated fair value	1,645,741	1,718,269
Non-GSE issuance REMICs and CMOs
Securities
Available-for-sale, amortized cost	10,118	11,296
Available-for-sale, Gross Unrealized Gains	7	9
Available-for-sale, Gross Unrealized Losses	(41)	(86)
Total available-for-sale securities	10,084	11,219
Held-to-maturity, amortized cost	5,041	5,791
Held-to-maturity, Gross Unrealized Gains	97	112
Held-to-maturity, estimated fair value	5,138	5,903
GSE pass-through certificates
Securities
Available-for-sale, amortized cost	19,468	20,348
Available-for-sale, Gross Unrealized Gains	1,025	1,029
Available-for-sale, Gross Unrealized Losses	(2)	(2)
Total available-for-sale securities	20,491	21,375
Held-to-maturity, amortized cost	209	257
Held-to-maturity, Gross Unrealized Gains	5	6
Held-to-maturity, Gross Unrealized Losses	(1)	(1)
Held-to-maturity, estimated fair value	213	262
Obligations of GSEs
Securities
Available-for-sale, amortized cost	98,672	98,670
Available-for-sale, Gross Unrealized Gains	85	214
Available-for-sale, Gross Unrealized Losses	(162)	(5)
Total available-for-sale securities	98,595	98,879
Held-to-maturity, amortized cost	80,923
Held-to-maturity, Gross Unrealized Gains	134
Held-to-maturity, Gross Unrealized Losses	(62)
Held-to-maturity, estimated fair value	80,995
Freddie Mac and Fannie Mae stock
Securities
Available-for-sale, amortized cost	15	15
Available-for-sale, Gross Unrealized Losses	(14)	(15)
Total available-for-sale securities	1
Other
Securities
Held-to-maturity, amortized cost	639	656
Held-to-maturity, estimated fair value	$ 639	$ 656

Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

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+ Details

- Definition

This item represents the cost of debt and equity securities, which are categorized neither as held-to-maturity nor trading, net of adjustments including accretion, amortization, collection of cash, previous other-than-temporary impairments recognized in earnings (less any cumulative-effect adjustments recognized, as defined), and fair value hedge accounting adjustments, if any.

+ References+ Details

- Definition

This item represents the gross unrealized gains for securities, at a point in time, which are categorized neither as held-to-maturity nor trading securities.

+ References+ Details

- Definition

For an unclassified balance sheet, this item represents investments in debt securities which are categorized as held-to-maturity. The held-to-maturity category is for those securities that the entity has the positive intent and ability to hold until maturity.

+ References

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+ Details

- Definition

This item represents the aggregate fair value of investments in debt securities as of the balance sheet date and which are categorized as held-to-maturity.

+ References+ Details

- 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+ Details

- 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