Federal Funds Purchased and Securities Sold under Agreements to Repurchase and Wholesale Borrowings (Details 1) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Federal Funds Purchased and Securities Sold under Agreements to Repurchase [Member]
Average balance during the year	$ 925,803	$ 907,015	$ 1,013,167
Weighted-average annual interest rate during the year	0.36%	0.49%	0.47%
Maximum month-end balance	1,014,720	1,034,200	1,350,475
Wholesale Borrowings [Member]
Average balance during the year	298,835	510,790	952,979
Weighted-average annual interest rate during the year	2.11%	2.74%	2.87%
Maximum month-end balance	$ 327,997	$ 716,091	$ 1,159,181