Investment Securities (Details 3) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Available for sale:
Fair value, less than 12 months	$ 2,889,527	$ 743,609
Unrealized losses, less than 12 months	(89,958)	(5,590)
Fair value, 12 months or more	59,204	43,353
Unrealized losses, 12 months or more	(13,251)	(12,254)
Fair value, total	2,948,731	786,962
Unrealized losses, total	(103,209)	(17,844)
Residential mortgage-backed securities
Available for sale:
Fair value, less than 12 months	2,836,648	738,492
Unrealized losses, less than 12 months	(87,735)	(5,476)
Fair value, 12 months or more	46,765	32,860
Unrealized losses, 12 months or more	(10,269)	(10,557)
Fair value, total	2,883,413	771,352
Unrealized losses, total	(98,004)	(16,033)
Obligations of states and political subdivisions
Available for sale:
Fair value, less than 12 months	42,360	5,117
Unrealized losses, less than 12 months	(1,993)	(114)
Fair value, 12 months or more	12,364	10,437
Unrealized losses, 12 months or more	(2,982)	(1,677)
Fair value, total	54,724	15,554
Unrealized losses, total	(4,975)	(1,791)
Equity Securities
Available for sale:
Fair value, less than 12 months	10,519
Unrealized losses, less than 12 months	(230)
Fair value, 12 months or more	75	56
Unrealized losses, 12 months or more		(20)
Fair value, total	10,594	56
Unrealized losses, total	$ (230)	$ (20)