Investment Securities AFS Securities Amortized Cost and Fair Value (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended	12 Months Ended
	Mar. 31, 2014	Dec. 31, 2013
Investment securities available for sale:
Investment securities available for sale, amortized cost	$ 5,277,650	$ 5,270,576
Investment securities available for sale, gross unrealized gains	87,561	88,043
Investment securities available for sale, gross unrealized losses	(87,303)	(108,034)
Investment securities available for sale, fair value	5,277,908	5,250,585
US Treasury Securities [Member]
Investment securities available for sale:
Investment securities available for sale, amortized cost	1,001	1,001
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	1,002	1,002
Obligations of state and political subdivisions (municipal securities) [Member]
Investment securities available for sale:
Investment securities available for sale, amortized cost	640,433	653,758
Investment securities available for sale, gross unrealized gains	25,539	23,855
Investment securities available for sale, gross unrealized losses	(628)	(1,533)
Investment securities available for sale, fair value	665,344	676,080
Government-Sponsored Enterprise (GSE) [Member]
Investment securities available for sale:
Investment securities available for sale, amortized cost	3,767,991	3,855,467
Investment securities available for sale, gross unrealized gains	60,240	61,542
Investment securities available for sale, gross unrealized losses	(58,989)	(78,579)
Investment securities available for sale, fair value	3,769,242	3,838,430
Private Label [Member]
Investment securities available for sale:
Investment securities available for sale, amortized cost	2,699	3,035
Investment securities available for sale, gross unrealized gains	16	16
Investment securities available for sale, gross unrealized losses	(18)	(37)
Investment securities available for sale, fair value	2,697	3,014
GNMA commercial mortgage-related securities [Member]
Investment securities available for sale:
Investment securities available for sale, amortized cost	839,488	673,555
Investment securities available for sale, gross unrealized gains	1,703	1,764
Investment securities available for sale, gross unrealized losses	(27,624)	(27,842)
Investment securities available for sale, fair value	813,567	647,477
Asset-backed Securities [Member]
Investment securities available for sale:
Investment securities available for sale, amortized cost	21,318	23,049
Investment securities available for sale, gross unrealized gains	0	10
Investment securities available for sale, gross unrealized losses	(36)	0
Investment securities available for sale, fair value	21,282	23,059
Other Debt And Other Equity Securities [Member]
Investment securities available for sale:
Investment securities available for sale, amortized cost	4,720	60,711
Investment securities available for sale, gross unrealized gains	62	855
Investment securities available for sale, gross unrealized losses	(8)	(43)
Investment securities available for sale, fair value	$ 4,774	$ 61,523