Loans and Loans Held for Sale - Restructured Loans for Periods Presented (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended				12 Months Ended
	Mar. 31, 2015		Mar. 31, 2014		Dec. 31, 2014
Financing Receivable, Modifications [Line Items]
Restructured loans	$ 4,585	[1]	$ 1,791	[1]
Performing TDRs [Member]
Financing Receivable, Modifications [Line Items]
Restructured loans	36,423				36,983
Performing TDRs [Member] | Commercial Real Estate [Member]
Financing Receivable, Modifications [Line Items]
Restructured loans	16,722				16,939
Performing TDRs [Member] | Commercial and Industrial [Member]
Financing Receivable, Modifications [Line Items]
Restructured loans	7,988				8,074
Performing TDRs [Member] | Commercial Construction [Member]
Financing Receivable, Modifications [Line Items]
Restructured loans	5,724				5,736
Performing TDRs [Member] | Residential Mortgage [Member]
Financing Receivable, Modifications [Line Items]
Restructured loans	2,507				2,839
Performing TDRs [Member] | Home Equity [Member]
Financing Receivable, Modifications [Line Items]
Restructured loans	3,438				3,342
Performing TDRs [Member] | Installment and Other Consumer [Member]
Financing Receivable, Modifications [Line Items]
Restructured loans	44				53
Nonperforming TDRs [Member]
Financing Receivable, Modifications [Line Items]
Restructured loans	9,916				5,436
Nonperforming TDRs [Member] | Commercial Real Estate [Member]
Financing Receivable, Modifications [Line Items]
Restructured loans	5,030				2,180
Nonperforming TDRs [Member] | Commercial and Industrial [Member]
Financing Receivable, Modifications [Line Items]
Restructured loans	1,772				356
Nonperforming TDRs [Member] | Commercial Construction [Member]
Financing Receivable, Modifications [Line Items]
Restructured loans	1,973				1,869
Nonperforming TDRs [Member] | Residential Mortgage [Member]
Financing Receivable, Modifications [Line Items]
Restructured loans	625				459
Nonperforming TDRs [Member] | Home Equity [Member]
Financing Receivable, Modifications [Line Items]
Restructured loans	510				562
Nonperforming TDRs [Member] | Installment and Other Consumer [Member]
Financing Receivable, Modifications [Line Items]
Restructured loans	6				10
Total TDRs [Member]
Financing Receivable, Modifications [Line Items]
Restructured loans	46,339				42,419
Total TDRs [Member] | Commercial Real Estate [Member]
Financing Receivable, Modifications [Line Items]
Restructured loans	21,752				19,119
Total TDRs [Member] | Commercial and Industrial [Member]
Financing Receivable, Modifications [Line Items]
Restructured loans	9,760				8,430
Total TDRs [Member] | Commercial Construction [Member]
Financing Receivable, Modifications [Line Items]
Restructured loans	7,697				7,605
Total TDRs [Member] | Residential Mortgage [Member]
Financing Receivable, Modifications [Line Items]
Restructured loans	3,132				3,298
Total TDRs [Member] | Home Equity [Member]
Financing Receivable, Modifications [Line Items]
Restructured loans	3,948				3,904
Total TDRs [Member] | Installment and Other Consumer [Member]
Financing Receivable, Modifications [Line Items]
Restructured loans	$ 50				$ 63

[1] Excludes loans that were fully paid off or fully charged-off by period end. The pre-modification balance represents the balance outstanding prior to modification. The post-modification balance represents the outstanding balance at period end.