Loans and Leases - Summary of Outstanding Principal Balance and Carrying Amount of Acquired Loans (Detail) - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
Accounts, Notes, Loans and Financing Receivable [Line Items]
Carrying amount	$ 11,626,787	$ 11,247,038
Accounted for under ASC 310-30 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Outstanding balance	1,423,534	1,597,558
Carrying amount	1,169,717	1,344,171
Accounted for under ASC 310-20 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Outstanding balance	219,358	242,488
Carrying amount	205,548	228,748
Acquired Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Outstanding balance	1,642,892	1,840,046
Carrying amount	$ 1,375,265	$ 1,572,919