Investment Securities (Details 3) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Available for sale:
Fair value, less than 12 months	$ 2,661,685	$ 743,609
Unrealized losses, less than 12 months	(87,343)	(5,590)
Fair value, 12 months or more	106,491	43,353
Unrealized losses, 12 months or more	(15,245)	(12,254)
Fair value, total	2,768,176	786,962
Unrealized losses, total	(102,588)	(17,844)
Residential mortgage-backed securities
Available for sale:
Fair value, less than 12 months	2,599,415	738,492
Unrealized losses, less than 12 months	(84,205)	(5,476)
Fair value, 12 months or more	94,376	32,860
Unrealized losses, 12 months or more	(11,376)	(10,557)
Fair value, total	2,693,791	771,352
Unrealized losses, total	(95,581)	(16,033)
Obligations of states and political subdivisions
Available for sale:
Fair value, less than 12 months	51,800	5,117
Unrealized losses, less than 12 months	(2,859)	(114)
Fair value, 12 months or more	12,044	10,437
Unrealized losses, 12 months or more	(3,865)	(1,677)
Fair value, total	63,844	15,554
Unrealized losses, total	(6,724)	(1,791)
Equity Securities
Available for sale:
Fair value, less than 12 months	10,470
Unrealized losses, less than 12 months	(279)
Fair value, 12 months or more	71	56
Unrealized losses, 12 months or more	(4)	(20)
Fair value, total	10,541	56
Unrealized losses, total	$ (283)	$ (20)