Unrealized Gross Losses and Estimated Fair values of Investment Securities by Length of Time that Individual Securities in Each Category in Continuous Loss Position (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Schedule of Available-for-sale Securities [Line Items]
Fair Value	$ 661	$ 47,989
Unrealized Losses	(2)	(336)
Fair Value	10,402	14,787
Unrealized Losses	(963)	(2,770)
Fair Value	11,063	62,776
Unrealized Losses	(965)	(3,106)
Mortgage-backed securities
Schedule of Available-for-sale Securities [Line Items]
Fair Value	311
Unrealized Losses	(1)
Fair Value	18
Fair Value	329
Unrealized Losses	(1)
Collateralized mortgage obligations
Schedule of Available-for-sale Securities [Line Items]
Fair Value	350	37,994
Unrealized Losses	(1)	(331)
Fair Value	350	37,994
Unrealized Losses	(1)	(331)
Private issue collateralized mortgage obligations
Schedule of Available-for-sale Securities [Line Items]
Fair Value	10,384	10,641
Unrealized Losses	(963)	(1,916)
Fair Value	10,384	10,641
Unrealized Losses	(963)	(1,916)
Obligations of U.S. government sponsored enterprises
Schedule of Available-for-sale Securities [Line Items]
Fair Value		9,995
Unrealized Losses		(5)
Fair Value		9,995
Unrealized Losses		(5)
Equity securities
Schedule of Available-for-sale Securities [Line Items]
Fair Value		4,146
Unrealized Losses		(854)
Fair Value		4,146
Unrealized Losses		$ (854)