Loans And Allowance For Loan Losses (Summary Of Information About Corporation's Purchased Credit-Impaired Loans) (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended	12 Months Ended
	Mar. 31, 2013	Dec. 31, 2012
Accounts, Notes, Loans and Financing Receivable [Line Items]
Balance at beginning of period, Contractual Receivable	$ 9,135
Balance at beginning of period, Accretable Yield	(254,153)	(51,706)
Balance at beginning of period	5,565
Accretion	8,909	47,686
Reclass from non-accretable difference	5,119	14,454
Balance at end of period, Contractual Receivable		9,135
Balance at end of period, Accretable Yield	(239,681)	(254,153)
Balance at end of period		5,565
Carrying Amount [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Balance at beginning of period	16,623	15,839
Acquisitions		5,565
Accretion	688	5,778
Payments received	(1,595)	(9,556)
Reclass from non-accretable difference
Disposals/transfers	(632)	(1,003)
Contractual interest
Balance at end of period	15,084	16,623
Accretable Yield [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Balance at beginning of period, Accretable Yield	(778)	(2,477)
Acquisitions, Accretable Yield		(589)
Accretion	688	5,778
Payments received, Accretable Yield
Reclass from non-accretable difference	(510)	(3,539)
Disposals/transfers	6	49
Contractual interest
Balance at end of period, Accretable Yield	(594)	(778)
Expected Cash Flows [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Balance at beginning of period	17,401	18,316
Acquisitions		6,154
Accretion
Payments received	(1,595)	(9,556)
Reclass from non-accretable difference	510	3,539
Disposals/transfers	(638)	(1,052)
Contractual interest
Balance at end of period	15,678	17,401
Non-Accretable Difference [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Balance at beginning of period	(23,733)	(33,377)
Acquisitions		(2,981)
Accretion
Payments received
Reclass from non-accretable difference	510	3,539
Disposals/transfers	5,436	11,442
Contractual interest	(444)	(2,356)
Balance at end of period	(18,321)	(23,733)
Contractual Receivable [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Balance at beginning of period, Contractual Receivable	41,134	51,693
Acquisitions, Contractual Receivable		9,135
Accretion
Payments received, Contractual Receivable	(1,595)	(9,556)
Reclass from non-accretable difference
Disposals/transfers	(6,074)	(12,494)
Contractual interest, Contractual Receivable	444	2,356
Balance at end of period, Contractual Receivable	$ 33,909	$ 41,134