Goodwill and Other Acquired Intangible Assets - Schedule of Definite-Lived Intangible Assets (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Goodwill [Line Items]
Gross Carrying Amount	$ 46,754	$ 46,754
Accumulated Amortization	(27,877)	(26,694)
Net Carrying Amount	18,877	20,060
Core deposit intangibles [Member]
Goodwill [Line Items]
Gross Carrying Amount	45,406	45,406
Accumulated Amortization	(27,409)	(26,284)
Net Carrying Amount	17,997	19,122
Customer relationship intangible asset [Member]
Goodwill [Line Items]
Gross Carrying Amount	1,348	1,348
Accumulated Amortization	(468)	(410)
Net Carrying Amount	$ 880	$ 938