Investment Securities - Schedule of Investment Securities (Details) (USD $) In Thousands, unless otherwise specified	0 Months Ended
Sep. 30, 2012	Dec. 31, 2011
Investment Securities
Schedule of Available-for-sale and Trading Securities [Line Items]
Available-for-sale Securities, Amortized Cost	$ 2,644,520	$ 2,203,928
Available-for-sale Securities, Unrealized Gains	17,525	10,993
Available-for-sale Securities, Unrealized Losses	(27,061)	(32,227)
Total available-for-sale	2,634,984	2,182,694
Marketable Securities, Amortized Cost	2,648,994	2,209,066
Marketable Securities, Unrealized Gains	17,525	10,993
Marketable Securities, Unrealized Losses	(30,191)	(35,569)
Marketable securities	2,636,328	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	(14,066)	(13,887)
Total available-for-sale	60,034	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	166,483	178,443
Available-for-sale Securities, Unrealized Gains	596	219
Available-for-sale Securities, Unrealized Losses	(34)	(102)
Total available-for-sale	167,045	178,560
Trading Securities Amortized Cost	4,474	5,138
Trading Securities, Unrealized Gains	0	0
Trading Securities, Unrealized Losses	(3,130)	(3,342)
Trading securities	1,344	1,796
Floating Interest Rate [Member] \| Corporate Debt Securities
Schedule of Available-for-sale and Trading Securities [Line Items]
Available-for-sale Securities, Amortized Cost	78,308	74,152
Available-for-sale Securities, Unrealized Gains	511	69
Available-for-sale Securities, Unrealized Losses	0	(388)
Total available-for-sale	78,819	73,833
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	734,406	759,567
Available-for-sale Securities, Unrealized Gains	9,168	4,852
Available-for-sale Securities, Unrealized Losses	(130)	(381)
Total available-for-sale	743,444	764,038
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	(12,830)	(17,438)
Total available-for-sale	57,170	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	49,992	38,000
Available-for-sale Securities, Unrealized Gains	64	32
Available-for-sale Securities, Unrealized Losses	0	0
Total available-for-sale	50,056	38,032
Fixed Interest Rate \| Asset-backed Securities
Schedule of Available-for-sale and Trading Securities [Line Items]
Available-for-sale Securities, Amortized Cost	9,735
Available-for-sale Securities, Unrealized Gains	0
Available-for-sale Securities, Unrealized Losses	0
Total available-for-sale	9,735
Fixed Interest Rate \| Corporate Debt Securities
Schedule of Available-for-sale and Trading Securities [Line Items]
Available-for-sale Securities, Amortized Cost	52,462	38,678
Available-for-sale Securities, Unrealized Gains	219	27
Available-for-sale Securities, Unrealized Losses	0	(6)
Total available-for-sale	52,681	38,699
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	2,331	3,106
Available-for-sale Securities, Unrealized Gains	206	254
Available-for-sale Securities, Unrealized Losses	0	0
Total available-for-sale	2,537	3,360
Fixed Interest Rate \| Commercial Paper [Member]
Schedule of Available-for-sale and Trading Securities [Line Items]
Available-for-sale Securities, Amortized Cost	19,995	9,999
Available-for-sale Securities, Unrealized Gains	2	1
Available-for-sale Securities, Unrealized Losses	0	0
Total available-for-sale	19,997	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	127,572	79,255
Available-for-sale Securities, Unrealized Gains	143	19
Available-for-sale Securities, Unrealized Losses	0	(21)
Total available-for-sale	127,715	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	1,179,754	798,966
Available-for-sale Securities, Unrealized Gains	139	304
Available-for-sale Securities, Unrealized Losses	(1)	(4)
Total available-for-sale	1,179,892	799,266
Fixed Interest Rate \| GSE Preferred Stock
Schedule of Available-for-sale and Trading Securities [Line Items]
Available-for-sale Securities, Amortized Cost	79,382	79,662
Available-for-sale Securities, Unrealized Gains	6,477	5,216
Available-for-sale Securities, Unrealized Losses	0	0
Total available-for-sale	$ 85,859	$ 84,878

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