Loans and leases and the allowance for credit losses (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2012	Dec. 31, 2011
Outstanding principal and carrying value of acquired loans recorded at fair value
Outstanding principal balance	$ 8,850,525	$ 9,203,366
Carrying amount	7,756,028	8,159,787
Commercial, financial, leasing, etc. [Member]
Outstanding principal and carrying value of acquired loans recorded at fair value
Carrying amount	1,259,609	1,331,198
Commercial real estate [Member]
Outstanding principal and carrying value of acquired loans recorded at fair value
Carrying amount	3,701,591	3,879,518
Residential real estate [Member]
Outstanding principal and carrying value of acquired loans recorded at fair value
Carrying amount	875,088	915,371
Consumer [Member]
Outstanding principal and carrying value of acquired loans recorded at fair value
Carrying amount	$ 1,919,740	$ 2,033,700