Investment Securities (Details 3) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2012 securities	Dec. 31, 2011 securities	Mar. 31, 2011 securities
Gross unrealized losses and fair value of securities
Fair Value, Less than 12 months	$ 181,287	$ 148,344	$ 839,793
Unrealized Losses, Less than 12 months	(1,902)	(506)	(5,792)
Number of Impaired Securities, Less than 12 months	64,000	26,000	151,000
Fair Value, 12 months or longer	46,659	44,385	50,141
Unrealized Losses, 12 months or longer	(14,843)	(17,256)	(12,166)
Number of Impaired Securities, 12 months or longer	9,000	10,000	10,000
Fair Value, Total	227,946	192,729	889,934
Unrealized Losses, Total	(16,745)	(17,762)	(17,958)
U.S. government agency debentures [Member]
Gross unrealized losses and fair value of securities
Fair Value, Less than 12 months	0		153,756
Unrealized Losses, Less than 12 months	0		(248)
Number of Impaired Securities, Less than 12 months	0		11,000
Fair Value, 12 months or longer	0		0
Unrealized Losses, 12 months or longer	0		0
Number of Impaired Securities, 12 months or longer	0		0
Fair Value, Total	0		153,756
Unrealized Losses, Total	0		(248)
US States and Political Subdivisions Debt Securities [Member]
Gross unrealized losses and fair value of securities
Fair Value, Less than 12 months	26,915	5,249	55,412
Unrealized Losses, Less than 12 months	(751)	50	(1,248)
Number of Impaired Securities, Less than 12 months	39,000	6,000	94,000
Fair Value, 12 months or longer	0	0	660
Unrealized Losses, 12 months or longer	0	0	(23)
Number of Impaired Securities, 12 months or longer	0	0	1,000
Fair Value, Total	26,915	5,249	56,072
Unrealized Losses, Total	(751)	50	(1,271)
Residential Mortgage Backed Securities Issued by US Government Sponsored Enterprises [Member]
Gross unrealized losses and fair value of securities
Fair Value, Less than 12 months	40,036	40,020	243,316
Unrealized Losses, Less than 12 months	(213)	129	(1,734)
Number of Impaired Securities, Less than 12 months	4,000	4,000	20,000
Fair Value, 12 months or longer	0	149	173
Unrealized Losses, 12 months or longer	0	2	(3)
Number of Impaired Securities, 12 months or longer	0	1,000	1,000
Fair Value, Total	40,036	40,169	243,489
Unrealized Losses, Total	(213)	131	(1,737)
Commercial Mortgage Backed Securities Issued by US Government Sponsored Enterprises [Member]
Gross unrealized losses and fair value of securities
Fair Value, Less than 12 months	12,329
Unrealized Losses, Less than 12 months	(60)
Number of Impaired Securities, Less than 12 months	2,000
Fair Value, 12 months or longer	0
Unrealized Losses, 12 months or longer	0
Number of Impaired Securities, 12 months or longer	0
Fair Value, Total	12,329
Unrealized Losses, Total	(60)
Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member]
Gross unrealized losses and fair value of securities
Fair Value, Less than 12 months	4,322	58,337	387,309
Unrealized Losses, Less than 12 months	(2)	(102)	(2,562)
Number of Impaired Securities, Less than 12 months	1,000	7,000	26,000
Fair Value, 12 months or longer	0	0	0
Unrealized Losses, 12 months or longer	0	0	0
Number of Impaired Securities, 12 months or longer	0	0	0
Fair Value, Total	4,322	58,337	387,309
Unrealized Losses, Total	(2)	(102)	(2,562)
Non-agency [Member]
Gross unrealized losses and fair value of securities
Fair Value, Less than 12 months	0	0
Unrealized Losses, Less than 12 months	0	0
Number of Impaired Securities, Less than 12 months	0	0
Fair Value, 12 months or longer	2	2
Unrealized Losses, 12 months or longer	0	0
Number of Impaired Securities, 12 months or longer	1,000	1,000
Fair Value, Total	2	2
Unrealized Losses, Total	0	0
Commercial Collateralized Mortgage Backed Securities Issued by US Government Sponsored Enterprises [Member]
Gross unrealized losses and fair value of securities
Fair Value, Less than 12 months	64,435	19,892
Unrealized Losses, Less than 12 months	(534)	(98)
Number of Impaired Securities, Less than 12 months	6,000	1,000
Fair Value, 12 months or longer	0	0
Unrealized Losses, 12 months or longer	0	0
Number of Impaired Securities, 12 months or longer	0	0
Fair Value, Total	64,435	19,892
Unrealized Losses, Total	(534)	(98)
Corporate Debt Securities [Member]
Gross unrealized losses and fair value of securities
Fair Value, Less than 12 months	33,250	24,846	0
Unrealized Losses, Less than 12 months	(342)	(127)	0
Number of Impaired Securities, Less than 12 months	12,000	8,000	0
Fair Value, 12 months or longer	46,657	44,234	49,308
Unrealized Losses, 12 months or longer	(14,843)	(17,254)	(12,140)
Number of Impaired Securities, 12 months or longer	8,000	8,000	8,000
Fair Value, Total	79,907	69,080	49,308
Unrealized Losses, Total	$ (15,185)	$ (17,381)	$ (12,140)