Changes in Core Deposit Intangible and Trust Relationship Intangible (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Accumulated Amortization
2012 amortization	$ (144)	$ (144)	$ (433)	$ (433)
Net
2012 amortization	(144)	(144)	(433)	(433)
Core Deposit Intangible
Total
Beginning Balance			14,444
Ending Balance	14,444		14,444
Accumulated Amortization
Beginning Balance			(11,432)
2012 amortization			(376)
Ending Balance	(11,808)		(11,808)
Net
Beginning Balance			3,012
2012 amortization			(376)
Ending Balance	2,636		2,636
Trust Relationship Intangible
Total
Beginning Balance			753
Ending Balance	753		753
Accumulated Amortization
Beginning Balance			(301)
2012 amortization			(57)
Ending Balance	(358)		(358)
Net
Beginning Balance			452
2012 amortization			(57)
Ending Balance	$ 395		$ 395