Gross Carrying Amounts and Accumulated Amortization of Intangible Assets and Goodwill (Detail) (USD $) In Thousands, unless otherwise specified	9 Months Ended	12 Months Ended
	Sep. 30, 2013	Dec. 31, 2012
Goodwill And Intangible Assets [Line Items]
Net Carrying Amount	$ 1,792	$ 3,163
Goodwill gross	84,171	84,808
Goodwill	84,171	84,808
Core Deposits
Goodwill And Intangible Assets [Line Items]
Gross Carrying Amount	9,716	9,716
Accumulated Amortization	(9,004)	(7,964)
Net Carrying Amount	712	1,752
Weighted average useful life	6 months	1 year 3 months 18 days
Other Intangible Assets
Goodwill And Intangible Assets [Line Items]
Gross Carrying Amount	8,623	8,611
Accumulated Amortization	(7,543)	(7,200)
Net Carrying Amount	1,080	1,411
Weighted average useful life	2 years 3 months 18 days	3 years 1 month 6 days
Amortization of Intangible Assets
Goodwill And Intangible Assets [Line Items]
Gross Carrying Amount	18,339	18,327
Accumulated Amortization	(16,547)	(15,164)
Net Carrying Amount	$ 1,792	$ 3,163