Securities (Securities Gains (Losses) (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended			6 Months Ended
	Jun. 30, 2012		Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Investment [Line Items]
Proceeds from sales			$ 33,723	$ 812	$ 60,493
Gross realized gains	253		848	379	1,272
Gross realized losses	(543)		(178)	(564)	(235)
Net realized (losses) gains	(290)	[1]	670	(185)	1,037
Income tax (benefit) provision on net realized (losses) gains	$ (115)		$ 266	$ (73)	$ 410

[1] Primarily relates to activity with our CRA investments and includes the amortization of tax credit investments under the effective yield method and adjustments for our portion of the of the investees' carrying value.