Loans and leases and the allowance for credit losses (Details 1) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2012
Summary of changes in Accretable Yield for acquired loans
Balance at the beginning of period	$ 838,765
Interest income	(81,387)
Reclassifications from (to) nonaccretable balance, net	424
Other (a)	12,229
Balance at end of period	770,031
Other [Member]
Summary of changes in Accretable Yield for acquired loans
Balance at the beginning of period	807,960
Interest income	(73,723)
Reclassifications from (to) nonaccretable balance, net	1,000
Other (a)	12,229
Balance at end of period	747,466
Purchase Impaired [Member]
Summary of changes in Accretable Yield for acquired loans
Balance at the beginning of period	30,805
Interest income	(7,664)
Reclassifications from (to) nonaccretable balance, net	(576)
Balance at end of period	$ 22,565