Investment Securities (Details 3) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010
Gross unrealized losses and fair value of securities
Fair Value, Less than 12 months	$ 148,344	$ 470,506
Unrealized Losses, Less than 12 months	(506)	(5,139)
Number of Impaired Securities, Less than 12 months	26	196
Fair Value, 12 months or longer	44,385	46,189
Unrealized Losses, 12 months or longer	(17,256)	(16,133)
Number of Impaired Securities, 12 months or longer	10	10
Fair Value, Total	192,729	516,695
Unrealized Losses, Total	(17,762)	(21,272)
U.S. government agency debentures [Member]
Gross unrealized losses and fair value of securities
Fair Value, Less than 12 months		109,238
Unrealized Losses, Less than 12 months		(194)
Number of Impaired Securities, Less than 12 months		8
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		109,238
Unrealized Losses, Total		(194)
U.S. States and political subdivisions [Member]
Gross unrealized losses and fair value of securities
Fair Value, Less than 12 months	5,249	105,530
Unrealized Losses, Less than 12 months	(50)	(2,095)
Number of Impaired Securities, Less than 12 months	6	164
Fair Value, 12 months or longer	0	665
Unrealized Losses, 12 months or longer	0	(24)
Number of Impaired Securities, 12 months or longer	0	1
Fair Value, Total	5,249	106,195
Unrealized Losses, Total	(50)	(2,119)
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	40,020	67,474
Unrealized Losses, Less than 12 months	(129)	(544)
Number of Impaired Securities, Less than 12 months	4	7
Fair Value, 12 months or longer	149	195
Unrealized Losses, 12 months or longer	(2)	(3)
Number of Impaired Securities, 12 months or longer	1	1
Fair Value, Total	40,169	67,669
Unrealized Losses, Total	(131)	(547)
Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member]
Gross unrealized losses and fair value of securities
Fair Value, Less than 12 months	58,337	188,264
Unrealized Losses, Less than 12 months	(102)	(2,306)
Number of Impaired Securities, Less than 12 months	7	17
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	58,337	188,264
Unrealized Losses, Total	(102)	(2,306)
Non-agency [Member]
Gross unrealized losses and fair value of securities
Fair Value, Less than 12 months	0
Unrealized Losses, Less than 12 months	0
Number of Impaired Securities, Less than 12 months	0
Fair Value, 12 months or longer	2
Unrealized Losses, 12 months or longer	0
Number of Impaired Securities, 12 months or longer	1
Fair Value, Total	2
Unrealized Losses, Total	0
Commercial Mortgage Backed Securities [Member]
Gross unrealized losses and fair value of securities
Fair Value, Less than 12 months	19,892
Unrealized Losses, Less than 12 months	(98)
Number of Impaired Securities, Less than 12 months	1
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	19,892
Unrealized Losses, Total	(98)
Corporate debt securities [Member]
Gross unrealized losses and fair value of securities
Fair Value, Less than 12 months	24,846	0
Unrealized Losses, Less than 12 months	(127)	0
Number of Impaired Securities, Less than 12 months	8	0
Fair Value, 12 months or longer	44,234	45,329
Unrealized Losses, 12 months or longer	(17,254)	(16,106)
Number of Impaired Securities, 12 months or longer	8	8
Fair Value, Total	69,080	45,329
Unrealized Losses, Total	$ (17,381)	$ (16,106)