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	Mar. 31, 2016	Dec. 31, 2015
Outstanding principal and carrying value of acquired loans recorded at fair value
Outstanding principal balance	$ 2,918,333	$ 3,122,935
Carrying amount	2,306,988	2,465,067
Commercial, Financial, Leasing, etc. [Member]
Outstanding principal and carrying value of acquired loans recorded at fair value
Carrying amount	71,577	78,847
Commercial Real Estate [Member]
Outstanding principal and carrying value of acquired loans recorded at fair value
Carrying amount	588,983	644,284
Residential Real Estate [Member]
Outstanding principal and carrying value of acquired loans recorded at fair value
Carrying amount	964,893	1,016,129
Consumer [Member]
Outstanding principal and carrying value of acquired loans recorded at fair value
Carrying amount	$ 681,535	$ 725,807