Investment Securities - Schedule of Investment Securities (Details) (USD $)			3 Months Ended		6 Months Ended							0 Months Ended
	Jun. 30, 2014	Dec. 31, 2013	Jun. 30, 2014 Investment Securities [Member]	Jun. 30, 2013 Investment Securities [Member]	Jun. 30, 2014 Investment Securities [Member]	Jun. 30, 2013 Investment Securities [Member]	Dec. 31, 2013 Investment Securities [Member]	Jun. 30, 2014 Available-for-sale Securities [Member] Investment Securities [Member]	Dec. 31, 2013 Available-for-sale Securities [Member] Investment Securities [Member]	Jun. 30, 2014 Floating Interest Rate [Member] Auction-rate certificates backed by Government guaranteed student loans [Member]	Dec. 31, 2013 Floating Interest Rate [Member] Auction-rate certificates backed by Government guaranteed student loans [Member]	Jun. 30, 2014 Floating Interest Rate [Member] Asset-backed Securities [Member]	Dec. 31, 2013 Floating Interest Rate [Member] Asset-backed Securities [Member]	Jun. 30, 2014 Floating Interest Rate [Member] Corporate Debt Securities [Member]	Dec. 31, 2013 Floating Interest Rate [Member] Corporate Debt Securities [Member]	Jun. 30, 2014 Floating Interest Rate [Member] Government/GSE Guaranteed Mortgage Backed Securities [Member]	Dec. 31, 2013 Floating Interest Rate [Member] Government/GSE Guaranteed Mortgage Backed Securities [Member]	Jun. 30, 2014 Floating Interest Rate [Member] GSE Subordinated Debt [Member}	Dec. 31, 2013 Floating Interest Rate [Member] GSE Subordinated Debt [Member}	Dec. 31, 2013 Floating Interest Rate [Member] Taxable Municipal Bonds [Member]	Jun. 30, 2014 Floating Interest Rate [Member] US Treasury Securities [Member]	Jun. 30, 2014 Floating Interest Rate [Member] Available-for-sale Securities [Member] Auction-rate certificates backed by Government guaranteed student loans [Member]	Dec. 31, 2013 Floating Interest Rate [Member] Available-for-sale Securities [Member] Auction-rate certificates backed by Government guaranteed student loans [Member]	Jun. 30, 2014 Floating Interest Rate [Member] Available-for-sale Securities [Member] Asset-backed Securities [Member]	Dec. 31, 2013 Floating Interest Rate [Member] Available-for-sale Securities [Member] Asset-backed Securities [Member]	Jun. 30, 2014 Floating Interest Rate [Member] Available-for-sale Securities [Member] Corporate Debt Securities [Member]	Dec. 31, 2013 Floating Interest Rate [Member] Available-for-sale Securities [Member] Corporate Debt Securities [Member]	Jun. 30, 2014 Floating Interest Rate [Member] Available-for-sale Securities [Member] Government/GSE Guaranteed Mortgage Backed Securities [Member]	Dec. 31, 2013 Floating Interest Rate [Member] Available-for-sale Securities [Member] Government/GSE Guaranteed Mortgage Backed Securities [Member]	Jun. 30, 2014 Floating Interest Rate [Member] Available-for-sale Securities [Member] GSE Subordinated Debt [Member}	Dec. 31, 2013 Floating Interest Rate [Member] Available-for-sale Securities [Member] GSE Subordinated Debt [Member}	Dec. 31, 2013 Floating Interest Rate [Member] Available-for-sale Securities [Member] Taxable Municipal Bonds [Member]	Jun. 30, 2014 Floating Interest Rate [Member] Available-for-sale Securities [Member] US Treasury Securities [Member]	Jun. 30, 2014 Floating Interest Rate [Member] Trading Securities [Member] Asset-backed Securities [Member]	Dec. 31, 2013 Floating Interest Rate [Member] Trading Securities [Member] Asset-backed Securities [Member]	Jun. 30, 2014 Fixed Interest Rate [Member] Corporate Debt Securities [Member]	Dec. 31, 2013 Fixed Interest Rate [Member] Corporate Debt Securities [Member]	Jun. 30, 2014 Fixed Interest Rate [Member] Government/GSE Guaranteed Mortgage Backed Securities [Member]		Dec. 31, 2013 Fixed Interest Rate [Member] Government/GSE Guaranteed Mortgage Backed Securities [Member]	Jun. 30, 2014 Fixed Interest Rate [Member] GSE Preferred Stock [Member]	Dec. 31, 2013 Fixed Interest Rate [Member] GSE Preferred Stock [Member]	Jun. 30, 2014 Fixed Interest Rate [Member] Taxable Municipal Bonds [Member]	Jun. 30, 2014 Fixed Interest Rate [Member] Senior Agency Debt Securities [Member]	Dec. 31, 2013 Fixed Interest Rate [Member] Senior Agency Debt Securities [Member]	Jun. 30, 2014 Fixed Interest Rate [Member] US Treasury Securities [Member]	Dec. 31, 2013 Fixed Interest Rate [Member] US Treasury Securities [Member]	Jun. 30, 2014 Fixed Interest Rate [Member] Available-for-sale Securities [Member] Corporate Debt Securities [Member]	Dec. 31, 2013 Fixed Interest Rate [Member] Available-for-sale Securities [Member] Corporate Debt Securities [Member]	Jun. 30, 2014 Fixed Interest Rate [Member] Available-for-sale Securities [Member] Government/GSE Guaranteed Mortgage Backed Securities [Member]	Dec. 31, 2013 Fixed Interest Rate [Member] Available-for-sale Securities [Member] Government/GSE Guaranteed Mortgage Backed Securities [Member]	Jun. 30, 2014 Fixed Interest Rate [Member] Available-for-sale Securities [Member] GSE Preferred Stock [Member]	Dec. 31, 2013 Fixed Interest Rate [Member] Available-for-sale Securities [Member] GSE Preferred Stock [Member]	Jun. 30, 2014 Fixed Interest Rate [Member] Available-for-sale Securities [Member] Taxable Municipal Bonds [Member]	Jun. 30, 2014 Fixed Interest Rate [Member] Available-for-sale Securities [Member] Senior Agency Debt Securities [Member]	Dec. 31, 2013 Fixed Interest Rate [Member] Available-for-sale Securities [Member] Senior Agency Debt Securities [Member]	Jun. 30, 2014 Fixed Interest Rate [Member] Available-for-sale Securities [Member] US Treasury Securities [Member]	Dec. 31, 2013 Fixed Interest Rate [Member] Available-for-sale Securities [Member] US Treasury Securities [Member]	Jun. 30, 2014 Fixed Interest Rate [Member] Available-for-sale Securities [Member] Interest-Only-Strip [Member]	Dec. 31, 2013 Fixed Interest Rate [Member] Available-for-sale Securities [Member] Interest-Only-Strip [Member]
Schedule of Available-for-sale and Trading Securities [Line Items]
Available-for-Sale Securities Unpaid Principal Balance			$ 2,307,390,000		$ 2,307,390,000		$ 2,475,407,000			$ 61,600,000	$ 74,100,000	$ 120,002,000	$ 166,185,000	$ 26,530,000	$ 109,345,000	$ 617,783,000	$ 612,413,000	$ 70,000,000	$ 70,000,000	$ 30,595,000	$ 75,000,000															$ 55,000,000	$ 55,000,000	$ 1,015,000		$ 1,173,000	$ 78,500,000	$ 78,500,000	$ 11,960,000	$ 200,000,000	$ 523,691,000	$ 990,000,000	$ 754,405,000
Debt Instrument, Unamortized Discount (Premium), Net			8,651,000		8,651,000		10,014,000	8,651,000	10,014,000													0	0	(138,000)	(217,000)	0	(3,000)	3,819,000	4,336,000	0	0	84,000	(14,000)	0	0													15,000	48,000	3,755,000	3,966,000	138,000	365,000	15,000	76,000	294,000	985,000	1,141,000	7,400,000	7,400,000
Available-for-sale Securities, Amortized Cost Basis			2,316,041,000		2,316,041,000		2,485,421,000			61,600,000	74,100,000	119,864,000	165,968,000	26,530,000	109,342,000	621,602,000	616,749,000	70,000,000	70,000,000	30,679,000	74,986,000															55,015,000	55,048,000	4,770,000		5,139,000	78,638,000	78,865,000	11,975,000	200,076,000	523,985,000	990,985,000	755,546,000
Available-for-Sale Gross Unrealized Gains			13,505,000		13,505,000		13,713,000			0	0	384,000	195,000	158,000	445,000	5,204,000	4,955,000	0	0	5,000	12,000															155,000	97,000	3,690,000		3,518,000	3,787,000	4,296,000	3,000	24,000	107,000	88,000	95,000
Available-for-sale Securities, Unrealized Losses			(13,583,000)		(13,583,000)		(15,987,000)			(6,624,000)	(8,815,000)	(4,000)	(59,000)	0	(18,000)	(262,000)	(435,000)	(6,615,000)	(6,615,000)	(3,000)	0															0	(4,000)	0		0	0	0	0	0	(30,000)	(78,000)	(8,000)
Available-for-sale Securities, Fair Value Disclosure			2,315,963,000		2,315,963,000		2,483,147,000			54,976,000	65,285,000	120,244,000	166,104,000	26,688,000	109,769,000	626,544,000	621,269,000	63,385,000	63,385,000	30,681,000	74,998,000															55,170,000	55,141,000	8,460,000	[1]	8,657,000	82,425,000	83,161,000	11,978,000	200,100,000	524,062,000	990,995,000	755,633,000
Trading Securities - Amount Outstanding												3,139,000	3,553,000
Trading Securities Amortized Cost												3,139,000	3,553,000
Trading Securities, Unrealized Gains												0	0
Trading Securities, Unrealized Losses												(2,259,000)	(2,625,000)
Trading, at fair value			880,000		880,000		928,000					880,000	928,000
Marketable Securities Unpaid Principal Balance			2,310,529,000		2,310,529,000		2,478,960,000
Marketable Securities, Amortized Cost			2,319,180,000		2,319,180,000		2,488,974,000
Marketable Securities, Unrealized Gains			13,505,000		13,505,000		13,713,000
Marketable Securities, Unrealized Losses			(15,842,000)		(15,842,000)		(18,612,000)
Marketable Securities			2,316,843,000		2,316,843,000		2,484,075,000
Derivative, Notional Amount	6,495,920,000	6,691,851,000																																				152,400,000		152,400,000
Proceeds from sale of available-for-sale investment securities			720,500,000	155,600,000	730,527,000	170,614,000
Available-for-sale Securities, Gross Realized Gains			$ 100,000	$ 3,100,000	$ 200,000	$ 3,100,000

[1] (1)Fair value includes $7.4 million of an interest-only security with a notional amount of $152.4 million.