Segment Reporting (Operating Segments and Reconciliation of Information to Condensed Consolidated Financial Statements) (Detail) (USD $)	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014	Dec. 31, 2014
Segment Reporting Information [Line Items]
Interest income	$ 38,072,000	$ 36,250,000
Interest expense	4,699,000	4,658,000
Provision (credit) for loan and lease losses	597,000	(982,000)
Non-interest income	13,159,000	11,249,000
Non-interest Expense	29,244,000	27,549,000
Income before income taxes	16,691,000	16,274,000
Income tax expense	5,466,000	5,346,000
Net income	11,225,000	10,928,000
Assets	4,401,380,000	4,168,998,000	4,397,132,000
Community Banking
Segment Reporting Information [Line Items]
Interest income	38,071,000	36,250,000
Interest expense	4,700,000	4,664,000
Provision (credit) for loan and lease losses	597,000	(982,000)
Non-interest income	9,836,000	8,015,000
Non-interest Expense	27,017,000	25,612,000
Income before income taxes	15,593,000	14,971,000
Income tax expense	5,034,000	4,831,000
Net income	10,559,000	10,140,000
Assets	4,403,060,000	4,206,353,000
Insurance
Segment Reporting Information [Line Items]
Interest income	1,000	2,000
Interest expense	0	0
Provision (credit) for loan and lease losses	0	0
Non-interest income	1,694,000	1,731,000
Non-interest Expense	1,383,000	1,192,000
Income before income taxes	312,000	541,000
Income tax expense	126,000	218,000
Net income	186,000	323,000
Assets	5,948,000	14,461,000
Investment Management
Segment Reporting Information [Line Items]
Interest income	1,000	4,000
Interest expense	0	0
Provision (credit) for loan and lease losses	0	0
Non-interest income	1,810,000	1,678,000
Non-interest Expense	1,025,000	920,000
Income before income taxes	786,000	762,000
Income tax expense	306,000	297,000
Net income	480,000	465,000
Assets	13,763,000	19,928,000
Intersegment Elimination
Segment Reporting Information [Line Items]
Interest income	(1,000)	(6,000)
Interest expense	(1,000)	(6,000)
Provision (credit) for loan and lease losses	0	0
Non-interest income	(181,000)	(175,000)
Non-interest Expense	(181,000)	(175,000)
Income before income taxes	0	0
Income tax expense	0	0
Net income	0	0
Assets	$ (21,391,000)	$ (71,744,000)