Investment Securities AFS Securities Amortized Cost and Fair Value (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Sep. 30, 2013	Dec. 31, 2012
Investment securities available for sale:
Investment securities available for sale, amortized cost	$ 4,844,155	$ 4,787,978
Investment securities available for sale, gross unrealized gains	93,370	143,700
Investment securities available for sale, gross unrealized losses	(97,490)	(4,920)
Investment securities available for sale, fair value	4,840,035	4,926,758
US Treasury Securities [Member]
Investment securities available for sale:
Investment securities available for sale, amortized cost	1,002	1,003
Investment securities available for sale, gross unrealized gains	1	1
Investment securities available for sale, gross unrealized losses	0	0
Investment securities available for sale, fair value	1,003	1,004
Obligations of state and political subdivisions (municipal securities) [Member]
Investment securities available for sale:
Investment securities available for sale, amortized cost	678,130	755,644
Investment securities available for sale, gross unrealized gains	25,747	45,599
Investment securities available for sale, gross unrealized losses	(1,150)	(55)
Investment securities available for sale, fair value	702,727	801,188
Government-Sponsored Enterprise (GSE) [Member]
Investment securities available for sale:
Investment securities available for sale, amortized cost	3,631,288	3,708,287
Investment securities available for sale, gross unrealized gains	64,987	93,595
Investment securities available for sale, gross unrealized losses	(79,195)	(3,727)
Investment securities available for sale, fair value	3,617,080	3,798,155
Private Label [Member]
Investment securities available for sale:
Investment securities available for sale, amortized cost	3,175	6,002
Investment securities available for sale, gross unrealized gains	20	147
Investment securities available for sale, gross unrealized losses	(36)	0
Investment securities available for sale, fair value	3,159	6,149
Commercial Mortgage Backed Securities [Member]
Investment securities available for sale:
Investment securities available for sale, amortized cost	444,534	226,420
Investment securities available for sale, gross unrealized gains	1,611	2,809
Investment securities available for sale, gross unrealized losses	(17,037)	(1,063)
Investment securities available for sale, fair value	429,108	228,166
Asset-backed Securities [Member]
Investment securities available for sale:
Investment securities available for sale, amortized cost	24,913
Investment securities available for sale, gross unrealized gains	11
Investment securities available for sale, gross unrealized losses	0
Investment securities available for sale, fair value	24,924
Other Debt And Other Equity Securities [Member]
Investment securities available for sale:
Investment securities available for sale, amortized cost	61,113	90,622
Investment securities available for sale, gross unrealized gains	993	1,549
Investment securities available for sale, gross unrealized losses	(72)	(75)
Investment securities available for sale, fair value	$ 62,034	$ 92,096