Loans and Leases and the Allowance for Credit Losses - Outstanding Principal Balance and Carrying Amount of Loans that is Included in Consolidated Balance Sheet (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Outstanding principal and carrying value of acquired loans recorded at fair value
Outstanding principal balance	$ 5,274,466	$ 6,705,120
Carrying amount	4,563,252	5,840,353
Commercial, Financial, Leasing, etc. [Member]
Outstanding principal and carrying value of acquired loans recorded at fair value
Carrying amount	730,743	928,107
Real Estate Commercial [Member]
Outstanding principal and carrying value of acquired loans recorded at fair value
Carrying amount	1,875,842	2,567,050
Residential Real Estate [Member]
Outstanding principal and carrying value of acquired loans recorded at fair value
Carrying amount	598,820	707,309
Consumer [Member]
Outstanding principal and carrying value of acquired loans recorded at fair value
Carrying amount	$ 1,357,847	$ 1,637,887