Loans and Leases and the Allowance for Credit Losses - Outstanding Principal Balance and Carrying Amount of Loans and Included in Consolidated Balance Sheet (Detail) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Outstanding principal and carrying value of acquired loans recorded at fair value
Outstanding principal balance	$ 1,842,739	$ 2,311,699
Carrying amount	1,378,168	1,804,271
Commercial, Financial, Leasing, etc. [Member]
Outstanding principal and carrying value of acquired loans recorded at fair value
Carrying amount	51,728	59,928
Commercial Real Estate [Member]
Outstanding principal and carrying value of acquired loans recorded at fair value
Carrying amount	368,661	456,820
Residential Real Estate [Member]
Outstanding principal and carrying value of acquired loans recorded at fair value
Carrying amount	717,139	799,802
Consumer [Member]
Outstanding principal and carrying value of acquired loans recorded at fair value
Carrying amount	$ 240,640	$ 487,721