Loans and the Allowance for Credit Losses - TDRs Defaulted Later Restructured (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2015 Defaults	Mar. 31, 2014 Defaults
Financing Receivable, Modifications [Line Items]
Number of Defaults	2	9
Recorded Investment	$ 69	$ 484
Residential Real Estate [Member]
Financing Receivable, Modifications [Line Items]
Number of Defaults		8
Recorded Investment		481
Home Equity [Member]
Financing Receivable, Modifications [Line Items]
Number of Defaults	1	1
Recorded Investment	42	3
Consumer [Member]
Financing Receivable, Modifications [Line Items]
Number of Defaults	1
Recorded Investment	$ 27