Segment Financial Information (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011	Dec. 31, 2011
Segment Reporting Information [Line Items]
Net Interest Income	$ 16,393	$ 16,203	$ 49,654	$ 47,574
Net Gains on Sales of Loans	941	863	2,330	1,651
Net Gains on Securities	598	0	692	1,045
Trust and Investment Product Fees	659	602	2,019	1,561
Insurance Revenues	1,469	1,261	4,218	4,600
Noncash Items:
Provision for Loan Losses	640	1,300	1,721	3,900
Depreciation and Amortization	1,085	1,217	3,584	3,902
Income Tax Expense (Benefit)	2,891	2,291	8,120	5,788
Segment Profit (Loss)	6,292	5,167	17,861	14,676
Segment Asset	1,962,298	1,871,083	1,962,298	1,871,083	1,873,767
Core Banking [Member]
Segment Reporting Information [Line Items]
Net Interest Income	16,909	16,726	51,213	49,155
Net Gains on Sales of Loans	941	863	2,330	1,651
Net Gains on Securities	598	0	692	0
Trust and Investment Product Fees	0	0	3	2
Insurance Revenues	3	16	19	56
Noncash Items:
Provision for Loan Losses	640	1,300	1,721	3,900
Depreciation and Amortization	941	1,072	3,145	3,392
Income Tax Expense (Benefit)	3,186	2,717	9,041	6,712
Segment Profit (Loss)	6,578	5,595	18,737	14,559
Segment Asset	1,964,276		1,964,276		1,875,417
Trust and Investment Advisory Services [Member]
Segment Reporting Information [Line Items]
Net Interest Income	6	7	16	14
Net Gains on Sales of Loans	0	0	0	0
Net Gains on Securities	0	0	0	0
Trust and Investment Product Fees	659	603	2,018	1,562
Insurance Revenues	5	7	32	9
Noncash Items:
Provision for Loan Losses	0	0	0	0
Depreciation and Amortization	6	4	16	21
Income Tax Expense (Benefit)	(45)	(100)	(103)	(247)
Segment Profit (Loss)	(71)	(151)	(168)	(374)
Segment Asset	11,724		11,724		11,801
Insurance [Member]
Segment Reporting Information [Line Items]
Net Interest Income	9	6	26	19
Net Gains on Sales of Loans	0	0	0	0
Net Gains on Securities	0	0	0	0
Trust and Investment Product Fees	0	0	0	0
Insurance Revenues	1,461	1,238	4,167	4,551
Noncash Items:
Provision for Loan Losses	0	0	0	0
Depreciation and Amortization	101	103	311	376
Income Tax Expense (Benefit)	70	(11)	176	319
Segment Profit (Loss)	100	(21)	245	418
Segment Asset	7,914		7,914		7,948
Other [Member]
Segment Reporting Information [Line Items]
Net Interest Income	(531)	(536)	(1,601)	(1,614)
Net Gains on Sales of Loans	0	0	0	0
Net Gains on Securities	0	0	0	1,045
Trust and Investment Product Fees	0	(1)	(2)	(3)
Insurance Revenues	0	0	0	(16)
Noncash Items:
Provision for Loan Losses	0	0	0	0
Depreciation and Amortization	37	38	112	113
Income Tax Expense (Benefit)	(320)	(315)	(994)	(996)
Segment Profit (Loss)	(315)	(256)	(953)	73
Segment Asset	$ (21,616)		$ (21,616)		$ (21,399)