Gross Carrying Amounts and Accumulated Amortization of Intangible Assets and Goodwill (Detail) (USD $) In Thousands, unless otherwise specified	6 Months Ended	12 Months Ended
	Jun. 30, 2013	Dec. 31, 2012
Goodwill And Intangible Assets [Line Items]
Net Carrying Amount	$ 2,241	$ 3,163
Goodwill gross	84,171	84,808
Goodwill	84,171	84,808
Amortization of Intangible Assets
Goodwill And Intangible Assets [Line Items]
Gross Carrying Amount	18,327	18,327
Accumulated Amortization	(16,086)	(15,164)
Net Carrying Amount	2,241	3,163
Amortization of Intangible Assets | Core Deposits
Goodwill And Intangible Assets [Line Items]
Gross Carrying Amount	9,716	9,716
Accumulated Amortization	(8,657)	(7,964)
Net Carrying Amount	1,059	1,752
Weighted average useful life	9 months 18 days	1 year 3 months 18 days
Amortization of Intangible Assets | Other Intangible Assets
Goodwill And Intangible Assets [Line Items]
Gross Carrying Amount	8,611	8,611
Accumulated Amortization	(7,429)	(7,200)
Net Carrying Amount	$ 1,182	$ 1,411
Weighted average useful life	2 years 7 months 6 days	3 years 1 month 6 days