Components of other intangible assets subject to amortization (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Finite-Lived Intangible Assets [Line Items]
Gross Amount	$ 95,572	$ 95,575
Finite Lived Intangible Assets Accumulated Amortization	63,908	56,556
Finite-Lived Intangible Assets, Net	31,664	39,019
Core Deposits Member
Finite-Lived Intangible Assets [Line Items]
Finite-Lived Core Deposits, Gross	77,885	77,885
Finite Lived Intangible Assets Accumulated Amortization	57,662	51,737
Finite-Lived Intangible Assets, Net	20,223	26,148
Customer Relationships Member
Finite-Lived Intangible Assets [Line Items]
Finite-Lived Customer Relationships, Gross	17,552	17,555
Finite Lived Intangible Assets Accumulated Amortization	6,114	4,712
Finite-Lived Intangible Assets, Net	11,438	12,843
Other Intangible Assets Member
Finite-Lived Intangible Assets [Line Items]
Other Finite-Lived Intangible Assets, Gross	135	135
Finite Lived Intangible Assets Accumulated Amortization	132	107
Finite-Lived Intangible Assets, Net	$ 3	$ 28