Amortized Cost And Fair Value Of Available For Sale And Held To Maturity Securities (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Gain (Loss) on Investments [Line Items]
Amortized Cost	$ 223,877	$ 282,647
Gross Unrealized Gain	12,714	11,256
Gross Unrealized Loss	(9)	(94)
Market Value	236,582	293,809
Amortized Cost	20,791	15,209
Gross Unrealized Gain	1,536	790
Gross Unrealized Loss	0	0
Market Value	22,327	15,999
U S Treasury And Government [Member]
Gain (Loss) on Investments [Line Items]
Amortized Cost	32,355	98,169
Gross Unrealized Gain	1,139	1,512
Gross Unrealized Loss	0	(59)
Market Value	33,494	99,622
Mortgage Backed Securities [Member]
Gain (Loss) on Investments [Line Items]
Amortized Cost	77,067	88,118
Gross Unrealized Gain	4,890	4,462
Gross Unrealized Loss	0	0
Market Value	81,957	92,580
Amortized Cost	15,254	9,676
Gross Unrealized Gain	860	410
Gross Unrealized Loss	0
Market Value	16,114	10,086
U S States And Political Subdivisions [Member]
Gain (Loss) on Investments [Line Items]
Amortized Cost	108,682	95,331
Gross Unrealized Gain	6,523	5,230
Gross Unrealized Loss	(9)	(35)
Market Value	115,196	100,526
Amortized Cost	5,537	5,533
Gross Unrealized Gain	676	380
Gross Unrealized Loss	0	0
Market Value	6,213	5,913
Corporate Debt Securities [Member]
Gain (Loss) on Investments [Line Items]
Amortized Cost	5,773	1,029
Gross Unrealized Gain	162	52
Gross Unrealized Loss	0	0
Market Value	$ 5,935	$ 1,081

Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

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+ Details

- Definition

This item represents the cost of debt and equity securities, which are categorized neither as held-to-maturity nor trading, net of adjustments including accretion, amortization, collection of cash, previous other-than-temporary impairments recognized in earnings (less any cumulative-effect adjustments recognized, as defined), and fair value hedge accounting adjustments, if any.

+ References+ Details

- Definition

This item represents the gross unrealized gains for securities, at a point in time, which are categorized neither as held-to-maturity nor trading securities.

+ References+ Details

- Definition

This item represents the aggregate fair value of investments in debt securities as of the balance sheet date and which are categorized as held-to-maturity.

+ References+ Details

- Definition

As of the balance sheet date, the excess of fair value over carrying value (amortized cost) of a debt security categorized as held-to-maturity, exclusive of dividend or interest income recognized but not yet received and exclusive of any write-downs for other-than-temporary impairment. Such item represents the gross unrecognized holding gain.

+ References+ Details

- Definition

As of the balance sheet date, the excess of carrying value (amortized cost) over fair value of a debt security categorized as held-to-maturity, exclusive of dividend or interest income recognized but not yet received and exclusive of any write-downs for other-than-temporary impairment. Such item represents the gross unrecognized holding loss.

+ References+ Details