Loans And Allowance For Loan Losses (Summary Of Information About Corporation's Purchased Credit-Impaired Loans) (Detail) (USD $) In Thousands, unless otherwise specified	9 Months Ended	12 Months Ended
	Sep. 30, 2012	Dec. 31, 2011
Accounts, Notes, Loans and Financing Receivable [Line Items]
Acquisitions	$ 6,154
Acquisitions	5,565
Balance at end of period, Contractual Receivable	8,989
Balance at end of period	5,565
Carrying Amount [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Balance at beginning of period	15,839	3,976
Acquisitions	5,565	17,464
Accretion	3,320	194
Payments received	(4,095)	(4,075)
Reclass from non-accretable difference
Disposals/transfers	(714)	(1,720)
Contractual interest
Balance at end of period	19,915	15,839
Accretable Yield [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Balance at beginning of period, Accretable Yield	(2,477)	(791)
Acquisitions, Accretable Yield	(589)	(2,025)
Accretion, Accretable Yield	3,320	903
Payments received, Accretable Yield
Reclass from non-accretable difference	(1,476)	(709)
Disposals/transfers, Accretable Yield	31	145
Contractual interest
Balance at end of period, Accretable Yield	(1,191)	(2,477)
Expected Cash Flows [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Balance at beginning of period	18,316	4,767
Acquisitions	6,154	19,489
Accretion
Payments received	(4,095)	(4,784)
Reclass from non-accretable difference	1,476	709
Disposals/transfers	(745)	(1,865)
Contractual interest
Balance at end of period	21,106	18,316
Non-Accretable Difference [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Balance at beginning of period	(33,377)	(15,589)
Acquisitions	(2,835)	(19,401)
Accretion
Payments received
Reclass from non-accretable difference	1,476	709
Disposals/transfers	2,798	4,263
Contractual interest	(2,368)	(3,359)
Balance at end of period	(34,306)	(33,377)
Contractual Receivable [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Balance at beginning of period, Contractual Receivable	51,693	20,356
Acquisitions, Contractual Receivable	8,989	38,890
Accretion, Contractual Receivable
Payments received, Contractual Receivable	(4,095)	(4,784)
Reclass from non-accretable difference
Disposals/transfers, Contractual Receivable	(3,543)	(6,128)
Contractual interest, Contractual Receivable	2,368	3,359
Balance at end of period, Contractual Receivable	$ 55,412	$ 51,693