Components of other intangible assets subject to amortization (Detail) - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
Finite-Lived Intangible Assets [Line Items]
Gross Amount	$ 112,128	$ 70,131
Finite Lived Intangible Assets Accumulated Amortization	43,387	38,650
Finite-Lived Intangible Assets, Net	68,741	31,481
Core Deposits Member
Finite-Lived Intangible Assets [Line Items]
Finite-Lived Core Deposits, Gross	74,252	50,679
Finite Lived Intangible Assets Accumulated Amortization	35,400	32,006
Finite-Lived Intangible Assets, Net	38,852	18,673
Customer Relationships Member
Finite-Lived Intangible Assets [Line Items]
Finite-Lived Customer Relationships, Gross	37,876	19,452
Finite Lived Intangible Assets Accumulated Amortization	7,987	6,644
Finite-Lived Intangible Assets, Net	$ 29,889	$ 12,808