Held-to-Maturity (HTM) Securities (Summary of Securities with Unrealized Losses) (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Fair Value:
Less than 12 Months	$ 0	$ 588,325
Greater than 12 Months	899,737	1,583,955
Fair Value	899,737	2,172,280
Unrealized Losses:
Less than 12 Months	0	(3,942)
Greater than 12 Months	(61,350)	(149,931)
Unrealized Losses	(61,350)	(153,873)
State and local agency obligations [Member]
Fair Value:
Less than 12 Months	0	0
Greater than 12 Months	157,553	195,899
Fair Value	157,553	195,899
Unrealized Losses:
Less than 12 Months	0	0
Greater than 12 Months	(19,022)	(34,291)
Unrealized Losses	(19,022)	(34,291)
Other US obligations MBS [Member]
Fair Value:
Less than 12 Months		90,308
Greater than 12 Months		154,860
Fair Value		245,168
Unrealized Losses:
Less than 12 Months		(16)
Greater than 12 Months		(75)
Unrealized Losses		(91)
GSE residential MBS [Member]
Fair Value:
Less than 12 Months	0	194,118
Greater than 12 Months	67,732	358,160
Fair Value	67,732	552,278
Unrealized Losses:
Less than 12 Months	0	(208)
Greater than 12 Months	(440)	(1,731)
Unrealized Losses	(440)	(1,939)
Private Label Residential MBS [Member]
Fair Value:
Less than 12 Months	0	303,899
Greater than 12 Months	663,865	861,942
Fair Value	663,865	1,165,841
Unrealized Losses:
Less than 12 Months	0	(3,718)
Greater than 12 Months	(39,551)	(109,354)
Unrealized Losses	(39,551)	(113,072)
HELOCs [Member]
Fair Value:
Less than 12 Months	0	0
Greater than 12 Months	10,587	13,094
Fair Value	10,587	13,094
Unrealized Losses:
Less than 12 Months	0	0
Greater than 12 Months	(2,337)	(4,480)
Unrealized Losses	(2,337)	(4,480)
Mortgage-backed Securities, Issued by Private Enterprises [Member]
Fair Value:
Less than 12 Months	0	303,899
Greater than 12 Months	674,452	875,036
Fair Value	674,452	1,178,935
Unrealized Losses:
Less than 12 Months	0	(3,718)
Greater than 12 Months	(41,888)	(113,834)
Unrealized Losses	(41,888)	(117,552)
MBS [Member]
Fair Value:
Less than 12 Months	0	588,325
Greater than 12 Months	742,184	1,388,056
Fair Value	742,184	1,976,381
Unrealized Losses:
Less than 12 Months	0	(3,942)
Greater than 12 Months	(42,328)	(115,640)
Unrealized Losses	$ (42,328)	$ (119,582)