Loans, Leases and Allowance for Credit Losses - Tabular Disclosure of Nonperforming Assets (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015		Dec. 31, 2014		Mar. 31, 2014	Dec. 31, 2013
Financing Receivable, Recorded Investment, Nonaccrual Status	$ 60,742	[1]	$ 67,659	[1]
Loans past due 90 days or more on accrual status	3,730		5,132
Troubled debt restructured loans	71,597	[2]	84,720	[2]
Total nonperforming loans	136,069		157,511
Other assets acquired through foreclosure, net	63,759		57,150		56,450	66,719
Total nonperforming assets	199,828		214,661
TDR loans [Member]
Financing Receivable, Recorded Investment, Nonaccrual Status	$ 50,700		$ 53,600

[1] Includes non-accrual TDR loans of $50.7 million and $53.6 million at March 31, 2015 and December 31, 2014, respectively.

[2] Includes accruing TDR loans only.