Allowance for Loan Losses, by Portfolio Segment (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	$ 25,770	$ 26,205
Provision for loan losses	1,142	922
Loans charged off	(2,759)	(1,562)
Recoveries credited to allowance	697	235
Net charge-offs	(2,062)	(1,327)
Ending balance	24,850	25,800
Commercial Loans
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	17,267	17,752
Provision for loan losses	483	262
Loans charged off	(783)	(253)
Recoveries credited to allowance	283	104
Net charge-offs	(500)	(149)
Ending balance	17,250	17,865
Consumer Real Estate
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	7,906	7,711
Provision for loan losses	480	618
Loans charged off	(1,396)	(1,105)
Recoveries credited to allowance	13	35
Net charge-offs	(1,383)	(1,070)
Ending balance	7,003	7,259
Consumer and Other
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	597	742
Provision for loan losses	179	42
Loans charged off	(580)	(204)
Recoveries credited to allowance	401	96
Net charge-offs	(179)	(108)
Ending balance	$ 597	$ 676