Investment Securities - Unrealized Loss Position (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2012	Dec. 31, 2011
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Unrealized loss position for less than 12 months, Fair Value	$ 879,342	$ 453,336
Available-for-sale Securities, Unrealized loss position for less than 12 months, Unrealized Loss	(406)	(880)
Available-for-sale Securities, Unrealized loss position for more than 12 months, Fair Value	122,302	130,184
Available-for-sale Securities, Unrealized loss position for more than 12 months, Unrealized Loss	(28,581)
Investment Securities
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Unrealized loss position for more than 12 months, Unrealized Loss	(28,600)	(31,347)
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of securities in unrealized loss position greater than twelve months	9	10
Available-for-sale securities in a loss position for more than 12 months, qualitative disclosure, percent of amortized cost	81.10%
Floating Interest Rate [Member] | Auction-rate certificates backed by Government guaranteed student loans
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Unrealized loss position for less than 12 months, Fair Value	0	0
Available-for-sale Securities, Unrealized loss position for less than 12 months, Unrealized Loss	0	0
Available-for-sale Securities, Unrealized loss position for more than 12 months, Fair Value	59,707	60,213
Available-for-sale Securities, Unrealized loss position for more than 12 months, Unrealized Loss	(14,393)	(13,887)
Floating Interest Rate [Member] | Asset-backed Securities
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Unrealized loss position for less than 12 months, Fair Value	24,304	63,496
Available-for-sale Securities, Unrealized loss position for less than 12 months, Unrealized Loss	(51)	(102)
Available-for-sale Securities, Unrealized loss position for more than 12 months, Fair Value	5,910	0
Available-for-sale Securities, Unrealized loss position for more than 12 months, Unrealized Loss	(16)	0
Floating Interest Rate [Member] | Government/GSE Guaranteed Mortgage Backed Securities
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Unrealized loss position for less than 12 months, Fair Value	91,149	235,454
Available-for-sale Securities, Unrealized loss position for less than 12 months, Unrealized Loss	(177)	(359)
Available-for-sale Securities, Unrealized loss position for more than 12 months, Fair Value	846	17,409
Available-for-sale Securities, Unrealized loss position for more than 12 months, Unrealized Loss	(11)	(22)
Floating Interest Rate [Member] | Corporate Debt Securities
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Unrealized loss position for less than 12 months, Fair Value	16,975	41,061
Available-for-sale Securities, Unrealized loss position for less than 12 months, Unrealized Loss	(26)	(388)
Available-for-sale Securities, Unrealized loss position for more than 12 months, Fair Value	0	0
Available-for-sale Securities, Unrealized loss position for more than 12 months, Unrealized Loss	0	0
Floating Interest Rate [Member] | GSE Subordinated Debt
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Unrealized loss position for less than 12 months, Fair Value	0	0
Available-for-sale Securities, Unrealized loss position for less than 12 months, Unrealized Loss	0	0
Available-for-sale Securities, Unrealized loss position for more than 12 months, Fair Value	55,839	52,562
Available-for-sale Securities, Unrealized loss position for more than 12 months, Unrealized Loss	(14,161)	(17,438)
Fixed Interest Rate | Corporate Debt Securities
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Unrealized loss position for less than 12 months, Fair Value	25,287	18,189
Available-for-sale Securities, Unrealized loss position for less than 12 months, Unrealized Loss	(30)	(6)
Available-for-sale Securities, Unrealized loss position for more than 12 months, Fair Value	0	0
Available-for-sale Securities, Unrealized loss position for more than 12 months, Unrealized Loss	0	0
Fixed Interest Rate | Senior Agency Debt Securities
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Unrealized loss position for less than 12 months, Fair Value		44,976
Available-for-sale Securities, Unrealized loss position for less than 12 months, Unrealized Loss		(21)
Available-for-sale Securities, Unrealized loss position for more than 12 months, Fair Value		0
Available-for-sale Securities, Unrealized loss position for more than 12 months, Unrealized Loss		0
Fixed Interest Rate | US Treasury Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Unrealized loss position for less than 12 months, Fair Value	721,627	50,160
Available-for-sale Securities, Unrealized loss position for less than 12 months, Unrealized Loss	(122)	(4)
Available-for-sale Securities, Unrealized loss position for more than 12 months, Fair Value	0	0
Available-for-sale Securities, Unrealized loss position for more than 12 months, Unrealized Loss	$ 0	$ 0