Held-to-Maturity Securities (Continuous Unrealized Loss Position) (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013		Dec. 31, 2012
Schedule of Held-to-maturity Securities [Line Items]
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	$ 585,387		$ 90,130
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Losses	(4,103)		(1,025)
Held-to-maturity Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	0		0
Held-to-maturity Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Losses	0		0
Held-to-maturity Securities, Continuous Unrealized Loss Position, Fair Value	585,387		90,130
Held-to-maturity Securities, Continuous Unrealized Loss Position, Aggregate Losses	(4,103)		(1,025)
Temporary Liquidity Guarantee Program [Member]
Schedule of Held-to-maturity Securities [Line Items]
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	25,578	[1]
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Losses	(1)	[1]
Held-to-maturity Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	0	[1]
Held-to-maturity Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Losses	0	[1]
Held-to-maturity Securities, Continuous Unrealized Loss Position, Fair Value	25,578	[1]
Held-to-maturity Securities, Continuous Unrealized Loss Position, Aggregate Losses	(1)	[1]
Held To Maturity Securities Other Than Mortgage Backed Securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	25,578
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Losses	(1)
Held-to-maturity Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	0
Held-to-maturity Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Losses	0
Held-to-maturity Securities, Continuous Unrealized Loss Position, Fair Value	25,578
Held-to-maturity Securities, Continuous Unrealized Loss Position, Aggregate Losses	(1)
Residential Mortgage Backed Securities, Issued by US Government Sponsored Enterprises [Member]
Schedule of Held-to-maturity Securities [Line Items]
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	559,809	[2]	90,130	[2]
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Losses	(4,102)	[2]	(1,025)	[2]
Held-to-maturity Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	0	[2]	0	[2]
Held-to-maturity Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Losses	0	[2]	0	[2]
Held-to-maturity Securities, Continuous Unrealized Loss Position, Fair Value	559,809	[2]	90,130	[2]
Held-to-maturity Securities, Continuous Unrealized Loss Position, Aggregate Losses	(4,102)	[2]	(1,025)	[2]
Collateralized Mortgage Backed Securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	559,809
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Losses	(4,102)
Held-to-maturity Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	0
Held-to-maturity Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Losses	0
Held-to-maturity Securities, Continuous Unrealized Loss Position, Fair Value	559,809
Held-to-maturity Securities, Continuous Unrealized Loss Position, Aggregate Losses	$ (4,102)

[1] Consists of debt securities issued and effectively guaranteed by Freddie Mac and/or Fannie Mae, which have the support of the U.S. government, although they are not obligations of the U.S. government.

[2] Consists of mortgage-backed securities issued and effectively guaranteed by Freddie Mac and/or Fannie Mae, which have the support of the U.S. government, although they are not obligations of the U.S. government.