Intangible Assets Subject to Amortization (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 143,704	$ 145,288
Accumulated Amortization	71,353	60,957
Net Carrying Amount	72,351	84,331
Core deposit intangible assets
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	36,497	36,497
Accumulated Amortization	29,984	28,629
Net Carrying Amount	6,513	7,868
Customer relationships
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	103,960	105,544
Accumulated Amortization	39,344	30,645
Net Carrying Amount	64,616	74,899
Other intangible assets
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	3,247	3,247
Accumulated Amortization	2,025	1,683
Net Carrying Amount	$ 1,222	$ 1,564