Changes In Intangible Assets (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 143,704	$ 143,704
Accumulated Amortization	78,356	74,901
Net Carrying Amount	65,348	68,803
Core deposit intangible assets [Member]
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	36,497	36,497
Accumulated Amortization	30,782	30,403
Net Carrying Amount	5,715	6,094
Customer relationships [Member]
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	103,960	103,960
Accumulated Amortization	45,401	42,399
Net Carrying Amount	58,559	61,561
Other intangible assets [Member]
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	3,247	3,247
Accumulated Amortization	2,173	2,099
Net Carrying Amount	$ 1,074	$ 1,148