Securities Sold Under Agreements to Repurchase and Other Short-term Borrowings (Additional Information for Short-term Borrowings) (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Assets Sold under Agreements to Repurchase [Line Items]
Securities sold under agreements to repurchase	$ 1,076,160	$ 941,706
Federal funds purchased	0	223,000
At end of year
Assets Sold under Agreements to Repurchase [Line Items]
Securities sold under agreements to repurchase	326,160	290,856	289,144
Securities sold under agreements to repurchase, Rate	0.15%	0.20%	0.25%
Federal funds purchased	0	223,000	236,500
Federal funds purchased, Rate	0.00%	0.12%	0.19%
Average during year
Assets Sold under Agreements to Repurchase [Line Items]
Securities sold under agreements to repurchase	306,294	310,355	312,728
Securities sold under agreements to repurchase, Rate	0.18%	0.22%	0.36%
Federal funds purchased	173,690	122,656	75,753
Federal funds purchased, Rate	0.17%	0.14%	0.21%
Highest month-end balance during year
Assets Sold under Agreements to Repurchase [Line Items]
Securities sold under agreements to repurchase	357,396	342,795	405,913
Securities sold under agreements to repurchase, Rate	0.00%	0.00%	0.00%
Federal funds purchased	$ 255,200	$ 282,000	$ 256,000
Federal funds purchased, Rate	0.00%	0.00%	0.00%