Investment Securities - Schedule of Investment Securities (Details) (USD $) In Thousands, unless otherwise specified	0 Months Ended
Jun. 30, 2012	Dec. 31, 2011
Investment Securities
Schedule of Available-for-sale and Trading Securities [Line Items]
Available-for-sale Securities, Amortized Cost	$ 2,508,369	$ 2,203,928
Available-for-sale Securities, Unrealized Gains	15,639	10,993
Available-for-sale Securities, Unrealized Losses	(28,987)	(32,227)
Total available-for-sale	2,495,021	2,182,694
Marketable Securities, Amortized Cost	2,512,980	2,209,066
Marketable Securities, Unrealized Gains	15,639	10,993
Marketable Securities, Unrealized Losses	(32,168)	(35,569)
Marketable securities	2,496,451	2,184,490
Floating Interest Rate [Member] \| Auction-rate certificates backed by Government guaranteed student loans
Schedule of Available-for-sale and Trading Securities [Line Items]
Available-for-sale Securities, Amortized Cost	74,100	74,100
Available-for-sale Securities, Unrealized Gains	0	0
Available-for-sale Securities, Unrealized Losses	(14,393)	(13,887)
Total available-for-sale	59,707	60,213
Floating Interest Rate [Member] \| Asset-backed Securities
Schedule of Available-for-sale and Trading Securities [Line Items]
Available-for-sale Securities, Amortized Cost	173,101	178,443
Available-for-sale Securities, Unrealized Gains	265	219
Available-for-sale Securities, Unrealized Losses	(67)	(102)
Total available-for-sale	173,299	178,560
Trading Securities Amortized Cost	4,611	5,138
Trading Securities, Unrealized Gains	0	0
Trading Securities, Unrealized Losses	(3,181)	(3,342)
Trading securities	1,430	1,796
Floating Interest Rate [Member] \| Government/GSE Guaranteed Mortgage Backed Securities
Schedule of Available-for-sale and Trading Securities [Line Items]
Available-for-sale Securities, Amortized Cost	755,343	759,567
Available-for-sale Securities, Unrealized Gains	7,212	4,852
Available-for-sale Securities, Unrealized Losses	(188)	(381)
Total available-for-sale	762,367	764,038
Floating Interest Rate [Member] \| Corporate Debt Securities
Schedule of Available-for-sale and Trading Securities [Line Items]
Available-for-sale Securities, Amortized Cost	86,293	74,152
Available-for-sale Securities, Unrealized Gains	360	69
Available-for-sale Securities, Unrealized Losses	(26)	(388)
Total available-for-sale	86,627	73,833
Floating Interest Rate [Member] \| GSE Subordinated Debt
Schedule of Available-for-sale and Trading Securities [Line Items]
Available-for-sale Securities, Amortized Cost	70,000	70,000
Available-for-sale Securities, Unrealized Gains	0	0
Available-for-sale Securities, Unrealized Losses	(14,161)	(17,438)
Total available-for-sale	55,839	52,562
Floating Interest Rate [Member] \| Senior Agency Debt Securities
Schedule of Available-for-sale and Trading Securities [Line Items]
Available-for-sale Securities, Amortized Cost	25,000	38,000
Available-for-sale Securities, Unrealized Gains	66	32
Available-for-sale Securities, Unrealized Losses	0	0
Total available-for-sale	25,066	38,032
Fixed Interest Rate \| Government/GSE Guaranteed Mortgage Backed Securities
Schedule of Available-for-sale and Trading Securities [Line Items]
Available-for-sale Securities, Amortized Cost	2,483	3,106
Available-for-sale Securities, Unrealized Gains	203	254
Available-for-sale Securities, Unrealized Losses	0	0
Total available-for-sale	2,686	3,360
Fixed Interest Rate \| Corporate Debt Securities
Schedule of Available-for-sale and Trading Securities [Line Items]
Available-for-sale Securities, Amortized Cost	57,723	38,678
Available-for-sale Securities, Unrealized Gains	64	27
Available-for-sale Securities, Unrealized Losses	(30)	(6)
Total available-for-sale	57,757	38,699
Fixed Interest Rate \| Commercial Paper
Schedule of Available-for-sale and Trading Securities [Line Items]
Available-for-sale Securities, Amortized Cost		9,999
Available-for-sale Securities, Unrealized Gains		1
Available-for-sale Securities, Unrealized Losses		0
Total available-for-sale		10,000
Fixed Interest Rate \| Senior Agency Debt Securities
Schedule of Available-for-sale and Trading Securities [Line Items]
Available-for-sale Securities, Amortized Cost	178,853	79,255
Available-for-sale Securities, Unrealized Gains	122	19
Available-for-sale Securities, Unrealized Losses	0	(21)
Total available-for-sale	178,975	79,253
Fixed Interest Rate \| US Treasury Securities [Member]
Schedule of Available-for-sale and Trading Securities [Line Items]
Available-for-sale Securities, Amortized Cost	1,005,995	798,966
Available-for-sale Securities, Unrealized Gains	33	304
Available-for-sale Securities, Unrealized Losses	(122)	(4)
Total available-for-sale	1,005,906	799,266
Fixed Interest Rate \| GSE Preferred Stock
Schedule of Available-for-sale and Trading Securities [Line Items]
Available-for-sale Securities, Amortized Cost	79,478	79,662
Available-for-sale Securities, Unrealized Gains	7,314	5,216
Available-for-sale Securities, Unrealized Losses	0	0
Total available-for-sale	$ 86,792	$ 84,878

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