Loans and the Allowance for Credit Losses - TDRs Defaulted Later Restructured (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013 Defaults	Jun. 30, 2012 Defaults	Jun. 30, 2013 Defaults	Jun. 30, 2012 Defaults
Financing Receivable, Modifications [Line Items]
Number of Defaults	6	4	31	10
Recorded Investment	$ 333	$ 528	$ 2,748	$ 2,251
Commercial Real Estate - Land and Construction [Member]
Financing Receivable, Modifications [Line Items]
Number of Defaults
Recorded Investment
Commercial Real Estate - Improved Property [Member]
Financing Receivable, Modifications [Line Items]
Number of Defaults		3	2	9
Recorded Investment		362	645	2,085
Commercial Real Estate [Member]
Financing Receivable, Modifications [Line Items]
Number of Defaults		3	2	9
Recorded Investment		362	645	2,085
Commercial and Industrial [Member]
Financing Receivable, Modifications [Line Items]
Number of Defaults		1	3	1
Recorded Investment		166	313	166
Residential Real Estate [Member]
Financing Receivable, Modifications [Line Items]
Number of Defaults	5		19
Recorded Investment	312		1,634
Home Equity [Member]
Financing Receivable, Modifications [Line Items]
Number of Defaults	1		6
Recorded Investment	21		124
Consumer [Member]
Financing Receivable, Modifications [Line Items]
Number of Defaults			1
Recorded Investment			$ 32