Allowance for Loan Losses, Allowance for Losses on Lending-Related Commitments and Impaired Loans Allowance for Loan Losses, Allowance for Losses on Lending-Related Commitments and Impaired Loans (Narrative) (Detail) (USD $)	3 Months Ended				12 Months Ended
	Mar. 31, 2014 contracts		Mar. 31, 2013 contracts		Mar. 31, 2014		Mar. 31, 2013		Dec. 31, 2013
Financing Receivable, Allowance for Credit Losses [Line Items]
Troubled debt restructuring modifications, number of count	6	[1],[2]	14	[1],[2]	27	[1],[3]	58	[1],[3]
Allowance for loan losses related to impaired loans	$ 8,197,000		$ 14,607,000		$ 8,197,000		$ 14,607,000		$ 8,265,000
Restructured loans	5,245,000	[1],[2]	2,277,000	[1],[2]	25,648,000	[1],[3]	35,106,000	[1],[3]
Weighted average extension term	13 months		21 months
Weighted average interest only term	9 months		8 months
Loan forgiveness	0		50,000
Weighted average stated interest rate, basis points	1.76%		1.53%
Financing Receivable [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Restructured loans	92,517,000		116,345,000		92,517,000		116,345,000		107,103,000
Troubled debt restructuring modifications, number of count	143
Allowance for loan losses related to impaired loans	4,000,000				4,000,000
Interest income	132,000		229,000
Modification to Interest Only Payments [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Troubled debt restructuring modifications, number of count	3	[1]	3	[1]
Restructured loans	$ 2,439,000	[1]	$ 308,000	[1]

[1] Balances represent the recorded investment in the loan at the time of the restructuring.

[2] TDRs may have more than one modification representing a concession. As such, TDRs during the period may be represented in more than one of the categories noted above.

[3] Total TDRs represent all loans restructured in TDRs during the previous twelve months from the date indicated.